NEW YORK (Reuters) - Four homeless people were killed in New York on Friday night with the hands of a young homeless man who beat them with a metal rod while they slept before authorities arrested him, police said.

Stephen Hughes, a Manhattan police official, told a news conference that the assailant, a 24-year-old homeless man who had assaulted a fifth man, seriously wounded the man and was taken to hospital.

He said the attack took place in the Chinatown neighborhood in southern Manhattan, and that the assailant was arrested thanks to eyewitness testimonies, adding that the metal bar he used in his attack was still in his possession when he was arrested.

Police investigator Michael Baldasano said the victims were probably asleep when they were assaulted.

More than 63,000 people are staying in emergency shelters in New York while another 4,000 sleep on the streets or in the subway, according to a humanitarian organization specializing in displaced persons.

Mental disorders, drug addiction, the lack of affordable housing and the difficulty of maintaining jobs are often the main causes of homelessness, according to the association.