(Updates with cause of fire, another child injured)
NEW YORK, April 20 (Reuters) - A house fire that left two young children dead early Easter Sunday in New York City was sparked accidentally, possibly by a child playing with a lighter or matches, emergency officials said.
The 4-year-old half-siblings, a boy and a girl, were at their grandfather's home in the city borough of Queens when the blaze broke out in the basement just before midnight on Saturday, a spokesman with the New York City Fire Department said.
The cause of the fire has been ruled accidental and the result of child-involved fire play, the spokesman said.
Investigators were looking at the possibility the blaze was sparked by a lighter or matches.
Four other people were injured in the blaze, including the 4-year-old sister of the boy, officials said.
A 55-year-old woman and a 63-year-old man, both in critical condition, were transported to a nearby hospital. Their identities have not yet been released, officials said.
A firefighter suffered mild injuries, the fire department spokesman said.
The two half-siblings were pronounced dead after they arrived at the hospital.
The children were regular visitors to their grandfather's house, neighbors told local media. It was unclear where and with whom they lived.
The fire took about an hour to extinguish and was contained to the basement, fire officials said.
(Reporting by Victoria Cavaliere; Editing by Barbara Goldberg and Chris Reese)