About 100 firefighters were working to put out a brush fire in a heavily wooded section of Prospect Park in Brooklyn on Friday night, prompting officials to warn residents to stay away as they used drones to identify hot spots.

“Every time the wind gusts up, we get an ember that creates more fire,” said Robert S. Tucker, the Fire Department’s commissioner. “This is going to be a long night, and we’re going to be in here until the morning.”

The Fire Department first received calls about the fire, in the Nethermead area southeast of the dog beach, around 6:40 p.m. No injuries had been reported as of 9:15 p.m., a spokesman said.

The department has not determined what caused the fire, but fire marshals will investigate once it is contained, he added.

Officials warned residents to stay away from the park and to close their windows because of the smoke. Commissioner Tucker said it was too difficult to evacuate the park because it was dark and firefighters were moving emergency equipment around, creating a risk that someone would be hurt inadvertently.

Mayor Eric Adams said in a post on X that the city was under a red flag warning for fire risk on Friday night because of dry conditions and strong winds.

“We urge all New Yorkers to stay vigilant and call 911 if they see a fire,” he said. “Any fire that sparks will catch and spread quickly in these conditions.”

Zachary Iscol, the city’s commissioner of emergency management, said New York City had been seeing an uptick in brush fires, which should be taken seriously because there had been so little rain.

New York City was put under a drought watch on Nov. 2. Mr. Iscol said he expected that a drought warning, a higher level of caution, was coming next, given that weather experts were anticipating a dry November and December in the region.

“This is something that we need to get ahead of,” he said, urging New Yorkers to conserve water.