Four homeless men were killed − and a fifth seriously injured − around Manhattan's Chinatown neighborhood when someone struck their heads with metal, apparently while they were sleeping, New York City, United States (U.S.), Police said Saturday.

A suspect, a 24-year-old man, who investigators believe also is homeless − is in custody, New York police Detective Annette Shelton said.

Officers found the victims early Saturday in three locations in or near Chinatown after someone called 911 to report one of the assaults shortly before 2 a.m., NYPD Assistant Chief Stephen Hughes said.

Investigators found a metal object -- possibly a pipe -- that they believe was used in the attacks, NYPD Deputy Chief Michael Baldassano said.

Police were scouring the crime scenes Saturday morning and weren't immediately able to explain why the attacks happened.

“The motive appears to be right now just ... random attacks," Baldassano said Saturday morning during a news conference.

Witnesses said they saw at least one attack, police say

The grisly discoveries began after someone called 911 at 1:49 a.m. to report an assault near a building at 2 Bowery in Chinatown, Hughes said.

The officers found a man -- later pronounced dead -- lying in the street with severe head trauma. A second man with head injuries approached the officers, and he was taken to a hospital in critical condition, Hughes said.

Two witnesses told police they saw a man in a black jacket and black pants strike someone numerous times with a metal object before fleeing, according to Hughes.

Officers started searching the area and found a man matching the attacker's description about a quarter-mile away, Hughes said. The man was taken into custody.

Officers expanded their search, and eventually found three other bodies -- two in front of 2 East Broadway, and one in front of 17 East Broadway, Hughes said.

All four bodies were found within roughly a two-block area.

The hospitalised man is 49 years old, Shelton said. The names of the victims and the person in custody weren't immediately released.

Officers' conversations with the injured man have been limited, but investigators hope to talk with him further, Baldassano said.

Baldassano and Hughes asked the public to come forward with any information about the attacks.

“I would ask ... anyone who may have seen something last night, or even in a few days in the past, or may have themselves been a victim of a crime like this, that they please contact the police,” Baldassano said. (CNN)

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