A 69-year-old man who apparently had been smoking in bed died early this morning after his mattress caught fire in his Kaka'ako apartment.

Firefighters responding to a sprinkler-activation alarm at the Honuakaha Housing Complex on Queen Street at 3:18 a.m. found the man's body in a sixth-floor studio apartment.

Fire Capt. Terry Seelig said the sprinkler in the apartment had extinguished the fire, which was confined to the mattress.

Seelig said smoking caused the blaze, which caused $5,000 in damage.

Bryan Cheplic of the city Emergency Services Department said paramedics pronounced the man dead at the scene at 3:42 a.m.

Police said the building manager was awakened by an activated fire alarm on the sixth floor and went to investigate.

They said the manager found water seeping out from under the victim's door, entered the apartment, found the bed burning and discovered the man on one side of the bed in a lifeless position.

The body was turned over to the city medical examiner. The man's name was not immediately disclosed.

The Honuakaha Housing Complex, separated from the Kakaako Fire Station only by the historic Royal Brewery building, was partially developed by the state in 1995.

It comprises 243 affordable housing units, 150 of which are designated as rentals for senior citizens.