A man was found after being trapped in vacant restaurant's grease vent for two days. Picture: Facebook

The call to firefighters came Wednesday morning after someone reported hearing a faint moaning, a cry for help coming from a vacant Chinese restaurant in a San Lorenzo strip mall.

When Alameda County from San Francisco Bay Area firefighters arrived, the moaning grew louder. It was coming from inside the kitchen, above the stove. There, inside a tight metal grease vent that led to the roof, they found the source of distress.

Firefighters cut away sheet metal and found a man covered in grease and soot. The man, whom authorities have not identified, told firefighters he had been stuck in the slick vent for two days.

It is unclear whether he was trying to break into the building, but he was arrested on suspicion of trespassing, said Alameda County Sheriff's Office spokesman Sergeant Ray Kelly.

The man was in good spirits despite his situation, Kelly added. Temperatures in the area dipped to six degrees Celsius on Tuesday night, according to the National Weather Service.

"One of his problems was he was stuck in a smooth metal circular tube, and his body was greased up. He could not get any traction," Kelly said. "I'm sure he tried."