NEW YORK (AP) - At least six people were killed and more were seriously injured Thursday night in a fire at an apartment building on a frigid night in the Bronx, according to a spokesman for New York City's mayor.

The blaze broke out at a five-story building, a block from the grounds of the Bronx Zoo. A spokesman for Mayor Bill de Blasio, Eric Phillips, told The Associated Press that there were six fatalities, but the eventual death toll was still uncertain.

"Will be more. Horrible," Phillips tweeted.

About 170 firefighters worked in bone-chilling cold, just 15 degrees, to rescue people from the building.

The mayor was headed for the scene, Phillips said, and officials were planning a news briefing.

Photographs and video of the building seemed to show that the fire, which was reported just before 7 p.m., appeared to be under control. No smoke or flames were visible, but windows on some upper floors were smashed and blackened.

"The smoke was crazy, people screaming, 'Get out!," a witness, Jamal Flicker, told the New York Post. "I heard a woman yelling, 'We're trapped, help!"

According to city records, the building had no elevator. Fire escapes were visible on the facade of the building.

One of the deadliest fires in recent city memory happened elsewhere in the Bronx in 2007. Nine children and one adult died in a blaze sparked by a space heater.

Copyright 2017 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.