Girl, 5, and Brother, 6, Are Killed in a Staten Island House Fire

A 5-year-old girl and her 6-year-old brother were killed early Friday when a fire engulfed the second story of their Staten Island home, the authorities said.

The children, whose names officials did not immediately release, were among six siblings in the house when the fire broke out around 10 a.m., officials said. Two other siblings, a 5-year-old boy and a 10-year-old boy, were in critical condition, and the remaining two were in stable condition with injuries that were not considered life-threatening, officials said on Friday afternoon. All six were 14 or younger, officials said.

The children’s mother, who was not at home when the fire began, was being treated for shock, officials said.

“A terrible tragedy has occurred here this morning,” Laura Kavanaugh, New York’s fire commissioner, said at a news conference near the site of the fire, on Van Duzer Street near the Wagner College campus.

Ms. Kavanaugh, who was joined at the news conference by, among others, Sheena Wright, New York City’s first deputy mayor, said the fire started at the back of the second floor and that the cause was under investigation but did not appear to be related to heating issues.

In response to a reporter’s question, Ms. Kavanaugh said there was no indication of an electric bike having played a role in the fire. The lithium-ion batteries used in such bikes have been linked to around 200 fires and six deaths in the city this year, according to fire officials.

Firefighters responding to the Staten Island fire around 10:20 a.m. on Friday encountered flames so fierce that “the fire was coming down the stairs” from the second floor, John J. Hodgens, the Fire Department’s chief of department, said.

Such an occurrence, he added, was “very rare.”

The six children were found unconscious on the second floor, Chief Hodgens said. One was pronounced dead at the scene; a second died after being taken to a hospital.

The fire was at least the second in New York City in the past few months to kill multiple children. In October, two boys, 10 and 12; a 10-month-old girl; and a man, 22, died after a fire broke out at a home in the Bronx.

Although there was no indication that a space heater or other means of warming the house had ignited the fire, Ms. Kavanaugh and other officials used the news conference to remind New Yorkers to heat their homes safely and to contact 311 if their heat was inadequate. Local temperatures are expected to drop well below freezing by early Saturday.

A malfunctioning space heater was identified as the cause of a January fire in a Bronx apartment tower that killed 17 people, including nine children, after an open apartment door allowed thick, black smoke to quickly fill the high-rise building.