Caliornia knife attacks
California police suspect the killer has a personal vendetta against homeless men. (Reuters)

Three homeless men have been stabbed to death in a series of killings thought to be motivated by a personal vendetta, California police said.

Authorities believe the murderer, who is believed to be aged between 18 and 25, is targeting and killing middle-aged men who sleep on the street.

Orange County police have warned those living on the street not to sleep alone or to seek shelter after the corpses of three victims were found with multiple stab wounds.

Police released CCTV footage of the suspect, who appeared to lie in wait for one of his victims at a shopping mall. James Patrick McGillvray, 53, had been sleeping rough in the city of Placentia when his mutilated body was found by a passer-by.

The body of the second victim, 42-year-old Lloyd Middaugh, was found near a cycle path in the city of Anaheim the following week.

The third victim, 57-year-old Paulus Cornelius Smit, was discovered in a stairwell near a public library in Yorba Linda.

All three men were all believed to have been asleep when they were murdered and no connection has been found among them except for their being homeless.

The Orange County Rescue Mission has been handing out torches and whistles to men on the streets, as well as encouraging them to sleep in groups or go to a shelter.

The spate of murders has prompted comparisons to two other serial killers who targeted the homeless in Southern California in the 1970s. The "Skid Row Slasher", Vaughn Greenwood, killed 11 men before his capture in 1975. Three years later, Bobby Maxwell killed a further 10 homeless men before he was discovered.