The New York City subway system suffered a slow-down in the Bronx on Sunday night after train cars detached with passengers on board.

Service on the 4 and 5 lines was suspended for several hours before it was fully restored around 1 a.m. Monday.

MTA explains what happened  

According to the MTA, there was a decoupling between the third and fourth car of a No. 4 train, meaning the cars separated. The NYPD said it happened at around 5:15 p.m. Sunday on the southbound tracks between 161st an 149th streets.

The FDNY said 12 units comprising 60 fire and EMS personnel arrived on the scene and had the situation under control within an hour. The MTA said customers on board the train were evacuated safely and no one was hurt.

The incident temporarily halted service on the 4 and 5 lines between the Bronx and Manhattan, while the MTA worked to move the train, which was said to have had a "mechanical problem." As of 11:30 p.m., service had resumed but with lengthy delays.

"It's very alarming and it's scary for passengers. We don't know if this could have been a rail problem or an issue with the train, itself," said Charlton D'Souza, the president of advocacy group Passengers United.

The MTA asked the public to refer to its website for service updates.  

Bronx residents sound off on weekend subway service

Workers at the 149th Street-Grand Concourse station were helping subway riders navigate, but the situation left Bronx residents frustrated.

Bridget Berkley anxiously waited on the platform at the station for her son, who she said was stuck on the train, in the dark, for over an hour.

"It's very panicky. I've been standing here stressed and worried for my son," Berkley said. "He's 14 years old, panicking, hyperventilating. He's going through the works. He just said the power went out. The conductor didn't say too much of anything of what's going on."

"If you live in the Bronx, you cannot reliably get home on the weekends, and often late at night. It is a travesty, frankly," resident Eric Forman said.

"Here in the Bronx, I think the 4/5, the service is stopping a lot of days during the weekends," Amanda Carneiro said, adding when asked what her message is to the MTA, "This is so essential to us and you should improve it."