Two newborns reportedly are among the more than 28,000 people infected with the novel coronavirus, which now has killed more than 560 people since it was detected in December.
The infants, one just 30 hours old, tested positive for the newly discovered virus on Wednesday at a children's hospital in Wuhan, China, the outbreak's epicenter. Both babies, believed to be the youngest to contract the virus, were reported in stable condition, but now concerns have been raised over whether mother-to-fetus transmissions are possible, according to China Daily, a state-owned newspaper.
At a news conference in Geneva on Thursday morning, Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, said 28,060 confirmed case of coronavirus have been reported in China, where 564 have died from it.
China National Health Commission officials said at a news conference Thursday morning that nearly two dozen cases have been confirmed in Hong Kong and that two patients have died there.
Ghebreyesus said another 225 confirmed cases have been reported outside of China, resulting in one death, a 44-year-old man in the Philippines.
In the United States, 12 confirmed coronavirus cases have been reported in Wisconsin, California, Washington, Arizona, Massachusetts and Illinois.
The World Health Organization has declared the outbreak a global health emergency.
Ghebreyesus urged the international community to invest in preparedness. He said the WHO is asking for $675 million for its Strategy Preparedness Response plan to tackle the virus on a global scale.
"Invest today or pay more later," he said.
A 12th coronavirus case in the United States was confirmed by health officials in Wisconsin on Wednesday. The patient, who recently visited Beijing, tested positive for the disease and has not been hospitalized, according to the Wisconsin Department of Health Services.
The individual is isolated at home and is in good condition. Health officials will monitor the patient's close contacts, as well as the health care workers who cared for the individual, for signs of illness.
"The risk of getting sick from 2019 novel coronavirus in Wisconsin is very low," Jeanne Ayers, a state health officer, said in a statement Wednesday.
The U.S. Centers for Disease Control and Prevention has shipped newly approved coronavirus tests to labs across the country so states can begin their own diagnostic testing instead of shipping all samples to CDC headquarters in Atlanta.
The United States has evacuated a number of its citizens from China amid the health crisis.
Two charter flights from Wuhan, containing about 350 passengers total, landed at the Travis Air Force Base in Northern California on Wednesday. One of the planes refueled at the base before continuing on to Marine Corps Air Station Miramar in San Diego, according to a statement from U.S. Army Lt. Col. Christian Mitchell.
All travelers will be screened by CDC medical personnel at their final destinations and placed under a federally mandated 14-day quarantine. The U.S. Department of Defense "will work closely with our interagency partners and continue to provide support to the situation as requested," Mitchell said.
Health officials in Nebraska and Texas are preparing for the arrival of Americans being rescued from Wuhan.
Officials said on Thursday 70 American patients would be quarantined at the Camp Ashland National Guard base in Ashland, Nebraska. Jeffrey Gold, chancellor of the Nebraska Medical Center, said the patients are being evacuated from the Wuhan area and all currently were healthy.
He said anyone showing symptoms of the virus after arriving in Nebraska would be taken to the University of Nebraska Medical Center and treated in isolation.
Capt. Jennifer McQuiston, deputy director of CDC's Division of High Consequence Pathogens and Pathology, said on Thursday that health officials are prepared to quarantine up to 250 people with American connections being evacuated from the Wuhan area at the Lackland Air Force Base near San Antonio.
McQuiston said the patients would be placed in a hotel, isolated from the rest of the base and ringed by a fence, guarded by federal marshals tasked with enforcing quarantines.
She said the U.S. State Department has identified about 1,000 Americans in China's Hubei Province, which includes Wuhan, who have requested help in evacuating to the United States.
The CDC confirmed Wednesday that its staff had completed health screenings on all 167 evacuees from China who had arrived at Marine Corps Air Station Miramar in San Diego. Three adults and one child "were determined to have fever or a cough that warranted them being transported to a local hospital for further evaluation," the CDC said in a statement.
The passengers who were quarantined last week after returning from Wuhan are expected to be released Feb. 11, officials said, as long as they and their immediate family members remain healthy.
"As of today, based on what we know about this virus, the far outside of incubation period is 14 days, "Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, said during a news conference Wednesday.
The new coronavirus causes symptoms similar to pneumonia -- sometimes mild, such as a slight cough, to more severe, including fever and difficulty breathing, according to the CDC. There's no vaccine yet for the virus.
Meanwhile, officials have expressed fears that the outbreak could disrupt the 2020 Summer Olympics slated to take place in Tokyo in July.
"I am extremely worried that the spread of the infectious disease could throw cold water on the momentum toward the Games," Toshiro Muto, chief executive of the Tokyo Olympic organizing committee, said during a meeting Wednesday with officials from the International Paralympic Committee. "I hope that it will be stamped out as soon as possible."
In an updated statement released Thursday, the Tokyo 2020 Press Office said "countermeasures" are being taken against the new coronavirus and other infectious diseases ahead of the Olympic Games to ensure a "safe and secure" event. For instance, the Japanese government has established the Novel Coronavirus Headquarters, while the Tokyo metropolitan government has set up an internal task force.
"Tokyo 2020 will continue to collaborate with all relevant organizations which carefully monitor any incidence of infectious diseases," the statement said, "and we will review any countermeasures that may be necessary with all relevant organizations."
Concerns about how the outbreak could affect the Olympics bubbled to the surface this week as at least 20 people aboard a cruise ship docked in Japan tested positive for the coronavirus.
Since arriving at the Japanese port of Yokohama on Monday, the Diamond Princess has been quarantined at sea while all passengers and crew aboard undergo health screenings. Those who tested positive were taken ashore to a hospital in the coastal prefecture of Kanagawa. Those patients include elderly people and foreign nationals, according to Japan's Ministry of Health, Labor and Welfare.
"Quarantine of the cruise ship continues to be implemented," the ministry said in a statement Thursday. "We are currently conducting a new coronavirus test for those who need it, and the results will be announced later."
A spokesperson for Princess Cruises, which operates the ship, said that those who tested positive included seven Japanese guests, three from Hong Kong, three Americans, two Canadians, two Australians, a guest from Taiwan, another from New Zealand and one crew member, from the Philippines.
There were 2,666 guests and 1,045 crew members aboard the ship. Approximately half are from Japan, with more than 400 passengers from the United States, according to the cruise line spokesperson.
"The health and safety of our guests and crew remains our top priority," the spokesperson said in a statement. "We continue to work closely with the Japan Ministry of Health on all protocols and procedures while ensuring the comfort of our guests."
The outbreak has caused several major U.S. airlines to suspend all flights to China, and U.S. companies and government agencies have evacuated staff from the country.
The University of Southern California and the University of Illinois at Urbana-Champaign announced this week they're suspending overseas programs in China after the U.S. State Department issued a Level 4 travel advisory for China on Jan. 30, warning people to avoid all travel to China.
ABC News' Erin Schumaker contributed to this report.