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New York City's positivity rate on Thursday jumped to 2.7%, "a worrisome number," Mayor Bill de Blasio said.

"It is literally twice yesterday," he said. "We cannot allow that number to keep growing. We really have to double down."

The mayor said there's no particular reason for the uptick. The city's seven-day positivity rate average is 1.92%.

De Blasio repeated his message that "people really should not travel for the holidays unless it’s absolutely necessary.”

“Unfortunately, pretty much everywhere is doing worse at fighting coronavirus,” he said. “And if you go someplace else, the chance of bringing it back with you is high."

The mayor also warned New Yorkers to avoid large gatherings for Halloween.

"People want to trick or treat outdoors, small groups with masks on, that’s great. Big gatherings, parties, that’s not great at all,” he said, warning, "we find out about them, we are going to break them up."

ABC News’ Aaron Katersky contributed to this report.

Officials in Oklahoma are warning that COVID-19 hospitalizations in the Sooner State could triple by the end of December if people don't change their personal behaviors or if local ordinances are not enacted.

Projections from the Institute for Health Metrics and Evaluation showed that if local mask and social distancing mandates don't change, cases, hospitalizations and deaths will all increase in Oklahoma.

"We elected leaders to protect us, that’s one of their main responsibilities," Dr. George Monks, president of the Oklahoma State Medical Association, told ABC News affiliate KTUL in Tulsa. "To protect their citizens, you may upset a minority number of citizens in your district, but you’ve got to step up."

If mandates are eased, those numbers could go up even more, officials said.

From Oct. 16-22, the number of cases in Oklahoma increased 20.2% and the week-over-week deaths increased 34.5%, according to the Oklahoma Department of Health.

Monks said IHME projects said the state would reach its maximum need of 2,711 beds for COVID patients on Dec. 28. It doesn't have to be that way, he said, if everyone wore masks.

"It is projected we will reach our maximum number of new COVID-19 cases per day on 12/09/2020 at 5,005 cases/day," Monks said on Twitter. "This number changes significantly if we implement universal masking."

In Oklahoma, more than 119,000 people have been diagnosed with COVID-19, with at least 1,286 deaths.

Researchers should know by December whether the vaccines in development are safe and effective, according to Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

Fauci added that he's "cautiously optimistic that we will have a safe and effective vaccine even though you can never make absolute predictions."

Hospitals in El Paso, Texas, are setting up tents to deal with the increase in COVID-19 patients as the U.S. sees a surge of new cases across the country.

All hospitals in the city, according to ABC News affiliate KVIA, have now started to build tents as of Wednesday night.

"Our hospitals continue to implement our surge plans to expand capacity to help manage the influx of Covid-19 patients to meet the rapidly expanding needs of El Paso," a Hospitals of Providence spokesperson told the station. "Medical tents will help decompress the Emergency Departments."

Texas Gov. Greg Abbott also announced on Wednesday that the El Paso Convention Center is being converted into a health care facility to expand hospital capacity in the area. "The State of Texas is also providing local hospitals with auxiliary medical units, medical staffing, and medical equipment," the Texas Division of Emergency Management said.

There were 845 new cases of COVID-29, which brings the city to at least 13,653 active cases as of Wednesday, according to local officials. There were three new deaths, which brings the death toll in El Paso to 583.

The 7-day rate of positivity in El Paso is 15.57%. There are 908 people currently hospitalized with coronavirus in the city, with 223 patients in ICUs and 111 on ventilators. There are 285 ICU beds in total in El Paso.

With the spike in cases in El Paso, city officials asked residents this week to largely stay at home. "For the next two weeks, we are asking you to please stay home unless for essential activities to reduce the spread of COVID-19 and prevent strain on our hospitals."

In Texas, there have been more than 911,000 diagnosed cases since the pandemic began, with at least 18,162 deaths.