Hayward police are looking for a man punched a 70-year-old man so hard in the head that he suffered significant brain trauma - and left him lying there for an hour while his group of friends partied nearby without doing anything to help.

The man was hit on Sunday before 7 p.m. as he was collecting recyclables at Kennedy Park in the Pavillion picnic area near the horseshoe pit, police said. Five days later, he has not regained consciousness at the hospital, police said.

At the time, police said there was a group of about 10 to 20 men and women using the picnic area - possibly celebrating a birthday.

A woman from the group starting talking to the elderly man. Moments later, one of the men in the partying group came up to the 70-year-old and "punched him in the head with enough force to cause him to fall to the ground and lose consciousness," police said.

The group continued their celebration while the elderly man lay unconscious on the ground. It wasn't until an hour later, when his wife came by looking for her husband, that he got help, police said.

Police emphasized that no one from the party group offered any help to the man, or tried to call for medical help.

The suspect is described as an African-American man standing six feet tall and weighing about 200 pounds. He left the park in a beige passenger vehicle, according to one witness at the scene. The victim is Chinese.

Police have not provided a motive for the beating.

Anyone with information is encouraged to call the Hayward Police Department at (510) 293-7034 or Inspector Rob Lampkin at (510) 293-7079.