NEW BRUNSWICK, N.J. (CBSNewYork) — A transformer explosion on Monday caused fire to rip through the main post office in New Brunswick, New Jersey.

As Christine Sloan reported, CBS2 was on the scene after the fire broke out around 11 a.m., as the smoke billowed out of the post office on Bayard Street

The post office is right next to police headquarters and the Middlesex County Prosecutor’s office.

“It sounded like a bomb, honestly, it was real quiet here, then boom,” witness Jochy Gomez told WCBS 880’s Jim Smith. “It was a lot of black smoke, the flames started off really small, after a while they picked up really high.”

“I was going to the P.O box – check my P.O. box — and I got to the rail. There was an explosion – boom!” added witness Maurice Fields. “I hear people screaming, running out the building. So I ran with them.”

One person captured video at the scene, while many others snapped pictures of flames shooting out of the building.

“It was like a huge explosion – a lot of smoke – a lot of smoke,” said Juan Velazquez, who was working when the fire broke out.

Everyone around felt the jolt and some took cover. The New Brunswick City Hall, and even the police department – except for dispatch – evacuated.

Authorities said an underground transformer exploded outside the post office.

“There was a transformer fire below the post office – electrical, obviously,” said New Brunswick police Capt. J.T. Miller.

The transformer blew up underground on the Kirkpatrick Street side of the post office. Everyone inside got out safely.

Michael Rizzolo, operations manager for the Northern New Jersey District of the U.S. Postal Service, said the evacuation happened at a rapid pace.

“Our employees reacted very quickly,” he said. “They pulled the fire alarm and exited without panic, and they made sure the customers were safely removed.”

Joe Stoltman was among those who evacuated the building.

“Our lights went dim. Our emergency lighting kicked on, there was, you know, you felt a slight shudder, but nothing really. We didn’t quite know what was happening,” he said.

Public Service Electric & Gas said the transformer exploded as crews were restoring power, causing an equipment failure. The company worked to restore power after the explosion.

“The post office will be without power until repairs are complete,” PSE&G said in a statement.

By midday, most of those evacuated had been allowed back into their buildings, thankful it wasn’t much worse.

Postal services for Bayard Street customers were temporarily relocated to the post office at 333 Handy St. Customers can pick up their mail by bringing photo identification. Normal postal services are expected to return at Bayard Street Wednesday. Mail delivery services were unaffected.