A homeless man was placed on life support after being beaten with a skateboard early Saturday in what witnesses told police appeared to be an unprovoked attack.

The 55-year-old victim was sleeping in an alley off El Cajon Boulevard near Idaho Street in North Park about 4:30 a.m. when he was assaulted, San Diego police said.

The victim was struck numerous times in the head with the skateboard and suffered serious head trauma, officials said. He was taken to a hospital.

As his condition remained grave, homicide investigators took over the case about 3 p.m., officials said.

Homicide Lt. Todd Griffin said medical staff determined that the man suffered internal head injuries consistent with an attack. He was placed on life support and is not expected to survive, Griffin said.

The man’s name was not released.

The assailant was described as white, in his late teens to early 20s, about 6 feet tall, with shoulder-length hair and wearing gray shorts and a dark shirt. He was seen fleeing in a white Honda, police said.