MONTCLAIR, N.J. (AP) _ An after-hours hold-up at a post office in a New York City suburb on Tuesday left four people dead and another person critically wounded.

The robber or robbers fled before police arrived.

Police said at least four men were killed at the post office in the Watchung Plaza shopping district near a New Jersey Transit train station.

All the victims were thought to be postal employees because the holdup occurred at just before 5 p.m., nearly an hour after the post office closed, Essex County Prosecutor Clifford Minor said.

Police Chief Thomas Russo said a postal worker who entered the office a few minutes before the shootings called police to say he thought he saw someone lying on the floor. When police arrived, the shooting had already occurred and the attacker or attackers had fled.

Howard Finney told WCBS Radio that he got off a commuter train and saw police with weapons drawn around the nearby post office.

He said he watched as police knocked down the front door of the post office around 5:15 p.m. A few minutes later, he said, about 10 people left the post office or an adjacent doorway and were rushed down the street by authorities.

He said one of the wounded was brought out on a stretcher about a half-hour later, carried to a nearby playground and then evacuated by helicopter.

A spokeswoman for University Hospital in Newark said a 44-year-old man was in critical condition with two gunshot wounds to the head.

Bill Murphy, 25, an employee at Watchung Booksellers a few stores down from the post office, said he heard what may have been three shots.

``I didn't know what they were. I thought it was a car backfiring. Then someone came in and told us what happened,'' he said.

A crowd quickly gathered on the street, he said.

``People were crying afterward,'' he said.

Children and parents in a doctor's office next to the post office were kept inside by police for safety in the aftermath of the shooting. When they were allowed to leave, some ran screaming from the office, giving rise to rumors that they had been hostages.

Postal inspector Peggy Hagar confirmed the deaths but would not comment on the circumstances of the shooting.

The post office where shootings occurred is a satellite to the main post office, which this month put in bullet-proof glass to protect its workers.

Montclair, about 15 miles west of New York City, is a mixed-income community of about 38,000 residents. Many people use the post office as a bank to cash checks and utility bills, so money is often on hand.

In 1991, a fired postal worker killed a former supervisor and her boyfriend in New Jersey at their home in Wayne _ 15 miles north of Montclair _ then went to the Ridgewood post office where he killed two mail handlers as they arrived for work. Joseph M. Harris surrendered after a 4 1/2-hour standoff with police.