Some of the 100 to 150 passengers on the early morning Metro-North train from suburban Poughkeepsie to Manhattan said they were jolted awake around 7:20 a.m. to screams and the frightening sensation of their compartment rolling over on a bend where the Hudson and Harlem rivers meet in the Bronx. When the motion stopped, four or five of the seven cars were off the rails in the latest, and deadliest, example of this year’s troubles for the nation’s second-biggest commuter railroad.

“Four people lost their lives today in the holiday season, right after Thanksgiving,” Gov. Andrew Cuomo said at a news conference. One of the four was found outside the train, officials said. Eleven of the injured were believed to be critically injured and another six seriously hurt, according to the Fire Department. The train operator was among the injured, Cuomo said.

The National Transportation Safety Board was en route to investigate, and Cuomo would not speculate about the causes of the crash until the federal agency issued its findings. Metropolitan Transportation Authority Chairman Thomas F. Prendergast noted that investigators would look at factors including the train, the track and signal system, the train operators and speed.

The big curve where the derailment occurred is in a slow-speed area. One passenger, Frank Tatulli told WABC-TV the train appeared to be going “a lot faster” than usual as it approached the curve coming into the Spuyten Duyvil station.

MTA spokeswoman Marjorie Anders said the train’s black box should be able to tell how fast the train was traveling, Anders said.

Many of those aboard the train, which left Poughkeepsie shortly before 6 a.m., were probably headed to New York for holiday shopping.

Joel Zaritsky was dozing as he traveled to the city for a dental convention.

“I woke up when the car started rolling several times. Then I saw the gravel coming at me, and I heard people screaming,” he told The Associated Press, holding his bloody right hand. “There was smoke everywhere and debris. People were thrown to the other side of the train.”

Three of the dead were found outside the train, and one was found inside, authorities said. Their families had not yet been notified.

Passengers were taken off the derailed train, with dozens of them bloodied and scratched, holding ice packs to their heads. The fire department said 130 firefighters responded to the scene.

Edwin Valero was in an apartment building above the accident. At first, he said, he didn’t notice that the train had flipped over.

“I didn’t realize it had been turned over until I saw a firefighter walking on the window,” he said.

Amtrak Empire service was halted between New York City and Albany after the derailment. Amtrak said its Northeast Corridor service between Boston and Washington was unaffected.

When the NTSB gives the go-ahead, the MTA will begin efforts to restore service, Prendergast said.

Sunday’s accident is the second passenger train derailment in six months for the rail service.

On May 17, an eastbound train derailed in Bridgeport, Conn., and was struck by a westbound train. The crash injured 73 passengers, two engineers and a conductor. Eleven days later, track foreman Robert Luden was struck and killed by a train in West Haven, Conn.

In July, a freight train full of garbage derailed while using a Metro-North line, and this fall service on Metro-North’s line between New York City and Connecticut was hobbled for days after a high-voltage feeder line failed.

Earlier this month, Metro-North’s chief engineer, Robert Puciloski, told members of the NTSB investigating the May derailment and Luden’s death that the railroad is “behind in several areas,” including a five-year schedule of cyclical maintenance that had not been conducted in the area of the Bridgeport derailment since 2005.

The NTSB issued an urgent recommendation to Metro-North that it use “redundant protection,” such as a procedure known as “shunting” in which crews attach a device to the rail in a work zone alerting the dispatcher to inform approaching trains to stop.