A man brutally shot and stabbed four family members inside a Manhattan apartment, killing his stepson and niece before dying himself in a fire that engulfed the home, authorities said.

The violence began about 8 p.m. Wednesday, when Lun Bao Zheng, 44, opened fire on his wife, nephew and stepson with a .22-caliber revolver inside their 21st-floor apartment on the Lower East Side (search), police said.

The wife and nephew fled, and Zheng began to attack the stepson, 19-year-old Jin Jie Ya, with a knife, said Sgt. Michael Wysokowski, a police department spokesman.

Sometime shortly afterward, an explosion rocked the apartment, causing a two-alarm fire that took about an hour to bring under control.

Inside, firefighters discovered the bodies of Zheng and Ya, along with a third victim — Xao Ying Chan, 27, Zheng's niece — whom police believe had been killed earlier.

The medical examiner's office would determine whether Zheng died in the blaze or killed himself before the explosion, police said.

Zheng's 43-year-old wife and 27-year-old nephew were taken to Bellevue Hospital Center (search) with gunshot and knife wounds, and were listed in stable condition.

Seventeen firefighters suffered minor injuries, including three who were taken to New York Weill-Cornell Medical Center (search) to be treated for burns and smoke inhalation.

There was no clear motive in the killings.

Fire marshals were investigating what caused the explosion.