Authorities said they were investigating whether a stove that was being used for heat ignited an early-morning fire in a Las Vegas apartment building on Saturday, killing six people and injuring 13 in the deadliest blaze in the city’s history.

The fire broke out around 4:13 a.m. near a stove in a first-floor unit, Timothy R. Szymanski, a spokesman for Las Vegas Fire and Rescue, said. Thick, poisonous smoke quickly traveled throughout the three-story, 42-unit building, inundating the upper floors, where several residents jumped from windows, he said.

Mr. Szymanski said witnesses told him one of those who jumped was pregnant. She was in critical condition, Mr. Szymanski said.

Several residents reported that they had been using their stoves for warmth because the heat in the building wasn’t working, he said.