Two firefighters were injured as about 70 battled flames that destroyed a vacant Bay Shore house where a blaze in April had killed a resident, the Brentwood Fire Department said.

The back of 17 Grant Ave. was ablaze when the first firefighter — Brentwood First Assistant Chief Michael Derbyshire — arrived shortly after getting the call about 3:30 p.m., officials said.

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Not long afterward, the rear of the house collapsed, but no one was found inside after an extensive search, said John Boyle, second assistant fire chief.

Two firefighters suffered minor burns and were airlifted to Stony Brook University Hospital, Boyle said. The hospital has a burn unit.

It took 80 minutes to get the blaze under control, with help from four other departments — Islip, West Islip, Bay Shore and East Brentwood, officials said. Brentwood Legion Ambulance also was at the scene, they said.

The cause is under investigation by Suffolk police arson detectives and the Islip Town fire marshal’s office.

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A fire that broke out in the basement apartment on the night of April 7 killed Curley Tutt, 62, who lived there, but several other adults and children in the home were able to escape, authorities said. Police said the cause did not appear to be criminal.