Two tornadoes passing through Oklahoma this evening left at least four people dead and destroyed dozens of houses, according to state and local officials.
News of the storm system gave the search for survivors in Joplin new urgency.
The storms are predicted to move into the Joplin area between 8 p.m. and 2 a.m. tonight, according to Bernie Rayno, expert senior meteorologist at Accuweather.com.
The city is still staggering from the EF-5 tornado that tore through the city on Sunday, the deadliest single tornado in more than 50 years.
Rayno said that a strengthening jet stream combined with "directional sheer," meaning changing wind speeds at different atmospheric heights, are textbook factors in tornado creation.
"There are not enough quotes to describe what could happen tonight," Rayno told ABC News.
The threat of more tornadoes comes as search and rescue teams struggle to find survivors. More than 750 people were injured in the storm Sunday that caused widespread devastation to the small midwestern town.
Want to help? Here is a list of organizations.
A Joplin, Mo., Tornado Recovery Facebook page has been created for people reaching out for information about lost loved ones.
Details have emerged that the massive tornado may have had two cyclones inside -- called "a multiple vortex."
"You don't go to bed at night thinking something like this would happen," Gov. Jay Nixon said this morning. "I was down here for graduation on Saturday, gym was filled with 4,000 of the happiest people you're ever going to see and the next thing I hear is that we've got a tornado coming and 24 hours later we're down here looking at this."
President Obama said this morning that he will visit the tornado-ravaged state of Missouri this weekend after he returns from Europe.
Speaking from the Ambassador's House in London, where he and Michelle Obama arrived earlier today, Obama called the outbreak of tornadoes "devastating and heartbreaking," while he reassured those affected by the storms that "every ounce of resources the federal government may have" will be used in recovery efforts.
"Our thoughts and prayers are with the families who are suffering at this moment," Obama said. "And all we can do is let them know that all of America cares deeply about them and that we are going to do absolutely everything we can to make sure that they recover."
Obama also acknowledged that more storms are headed for the region today, as a warning of new tornado outbreaks was issued for the central region of the United States by an Oklahoma storm prediction center. Long-form, long-track, very powerful tornadoes are expected throughout Tuesday.
The greatest threat for tornadoes stretches from Dallas to Kansas City, according to the report. The area includes Joplin, Mo., where rescue workers are racing to salvage survivors from the wreckage left by a tornado that destroyed an estimated 30 percent of the city on Sunday.
The massive Joplin tornado was rated as an EF-5, the strongest classification, with winds ranging above 200 mph. The nearly mile-wide funnel touched down at 5:41 p.m. CT Sunday and blasted a six mile wide path through the city and left trapped survivors crying out for help this morning.
The tornado that struck Flint, Mich., on June 8, 1953 and killed 116 people had been the deadliest single tornado on record since the National Oceanic and Atmospheric Administration began keeping track of tornado fatalities in 1950.
The lethal twister has also made 2011 the deadliest year for tornadoes since 1953, with 454 deaths from 1,000 tornadoes so far, according to NOAA.
April also set a record as the deadliest month with 361 tornado-related deaths, according to NOAA's records.
Rescuers shifted through the rubble of six miles of debris and more than 2000 damaged buildings on Monday, looking for survivors as high winds and hail continues to plague the area.
"This a community. We are more than a city ... we do things together," Joplin Mayor Mike Woolston told ABC News' Diane Sawyer. "The city sheltered a number of people the first night, but it was a hundred or so, something like that. Given that we had 2,000 structures that are damaged, you wonder where those people went. Well, they're staying with friends, they're staying with family, some of them may be staying with complete strangers they don't know but may have taken them in. The amount of donations we've had is overwhelming."
Helping among the relief efforts is TLC's "19 Kids and Counting's" Josh Duggar, a volunteer firefighter.
"The whole town is just torn apart. And I think you can just sense the people, there's a sense of 'we can do this, we're going to unite together and take care of this,'" Duggar told "Good Morning America."
Doug Westoff and his "Missouri Task Force One" desperately searched for anyone still living among these cars in the parking lot of a local Wal-Mart.
"It's mother nature, we just react to it and do the best we can," Westoff said.
So far, 9 people have been pulled alive from the wreckage. "[We] want to focus on the fact that we believe there are still rescues out there … and we want to support the men and women that are on the ground out there, literally going foot by foot searching for folks," Gov. Nixon said Monday.
Nixon declared a state of emergency Sunday evening and activated the Missouri National Guard in response to the destruction.
Five patients and one visitor were killed at St. John's Regional Medical Center in Joplin when it took a direct hit from the tornado. Patients and staff have been evacuated as damage suffered during the storm has affected the structural integrity of the building. Every window in the facility was blown out and the top two floors were blown off, ABC News affiliate KMBC reported.
Dr. Ronnie Smalling was inside the hospital when the tornado began to form overhead.
"I went over to the window and the clouds were black, wind was blowing and I began to see things fall out of the sky. I screamed at the staff to get away from windows and into the interior. The windows began to pop, and it began to sound like a freight train, just a sucking sound," Smalling told "Good Morning America."
"It was like if you were to dive 30 feet below the water. I thought I may die, that this may be my time. It lasted 90 seconds, and we heard the hail," he said.
Hospital spokeswoman Cora Scott told the station that 183 patients were in the hospital at the time and the facility only had five minutes warning that the tornado would strike. More than 100 patients have since been evacuated to other hospitals, Scott said.
The hospital declared a "condition gray" -- meaning patients, relatives and staff were instructed to leave their rooms to take cover in protected areas.
Seven people have been reported dead at a nursing home, according to police reports.
State and local law enforcement agencies, including fire mutual aid, are coordinating search and rescue and recovery operations. The Missouri State Highway Patrol sent troopers from other regions to help local officers in southern Missouri deal with the destruction, the governor's office said in a statement.
Keith Stammer, emergency management director for the city of Joplin, told "Good Morning America" that all 25 of the city's sirens did activate, and that there was a 20-minute notice from when the sirens were activated before there was a first report of a tornado strike.
"At the moment its surreal, our landmarks are gone -- road signs, places where you know to turn -- we're doing search and rescue, going house to house on that six mile strip," Stammer told "GMA."
Federal Emergency Management Agency Region VII set up a response coordination center and sent a liaison team to the Missouri state emergency communications center, according to a FEMA official.
"Basically it's an all-out effort to get all of the most important resources available for this type of situation down as soon as possible," a state emergency management representative said.
In total, 70 tornadoes were produced by the storm system since Friday, including at least 47 tornadoes Sunday. Tornadoes were reported in seven states from the Canadian border to Oklahoma. Warnings and watches were posted from Texas to Michigan.
ABC News' Jackie Meretsky contributed to this report.