NEW YORK－Investigators searched early on Friday for the cause of a blaze that ripped through an apartment building in the borough of the Bronx, killing at least 12 people including an infant, in the city's deadliest fire in over a quarter of a century.

The fire broke out before 7 pm on Thursday on the first floor of a brick building and quickly spread upstairs, city Fire Commissioner Daniel Nigro said at a news conference with Mayor Bill de Blasio.

"We're here at the scene of an unspeakable tragedy. In the middle of the holiday season is a time when families are together. Tonight, here in the Bronx, there are families that have been torn apart," De Blasio said.

Four people were in the hospital in critical condition, the mayor said. Authorities said firefighters rescued 12 people from the building.

"People died on various floors of the apartments, ranging in age from 1 to over 50," Nigro said. "In a department that is surely no stranger to tragedy, we're shocked by the lives lost."

Two of the dead were found in a bathtub, according to cable news station NY1.

"People were screaming and that's how we knew there was trouble," eyewitness Kimberly Wilkins told WCBS-TV, an affiliate of CBS News. "People were screaming, 'Fire. Help. Fire. Help.'"

The blaze erupted in the Belmont section of the Bronx, a primarily residential, closeknit neighborhood known as the "Little Italy" of the borough, adjacent to the Bronx Zoo and Fordham University.

Excluding the Sept 11, 2001, terrorist attacks, it was the worst fire in the city since 87 people were killed at a social club fire in the Bronx in 1990.

New York is going through a bitter cold snap and high winds that, according to one media account, stoked flames inside the building as residents flung open doors and windows.

Wherever fire hoses sprayed, the ground was covered with sheets of ice, according to an NY1 reporter.

More than 160 firefighters responded to the four-alarm blaze, the New York City Fire Department said.

Reuters-AP