About 40 to 50 young males attacked a 50-year-old man riding a bicycle and beat him unconscious, police said.

The motive for the attack Tuesday evening was not known and police were still interviewing witnesses, Lt. Tom Hemingway said. No arrests have been made.

Witnesses told investigators the attackers knocked the man off his bike and began beating him. Police said he was hit in the head with a bottle and then kicked and punched as he lay in the street.

His stolen bike was found later. The man remained hospitalized Wednesday.

Hemingway said the unseasonably warm weather drew many people outdoors, and police had been dispersing large groups of young people in the city all afternoon.

"You just can't be everywhere at once," Hemingway said. "We had officers just a couple of blocks away when the attack happened."

Kalamazoo's high on Tuesday was 63 degrees, according to the National Weather Service. Its average high for the date is 35.