Fourteen people are dead and 18 others are seriously injured after an accident involving a tour bus returning to New York City early Saturday morning from a casino in Connecticut.

The crash occurred at 5:30 a.m. ET on Interstate 95 in the Bronx. It left a scene of carnage and closed the southbound side of the highway for hours while emergency workers removed bodies and attended to critically injured survivors.

Police say the driver told them that he was driving alongside a tractor trailer, which either swerved towards or hit the bus. That caused the driver to swerve to the right, hitting a guard rail. The bus then toppled and struck a highway sign support pole. The pole sheared the bus almost from front to back along the window line, peeling the roof off all the way to the rear wheels.

In addition to the 14 who were killed, seven other passengers were critically hurt.

It is not known how fast the bus was going when it struck the pole.

"That's something that will have to be calculated by investigators," New York City police commissioner Raymond Kelly said at a press conference. "Obviously, it was a significant rate of speed."

Police are still searching for the driver of the truck, which did not stop after the crash.

"We are attempting to locate the truck and truck driver," said Kelly. "We apparently have some numbers from a licence plate, but we're not prepared to put it out at this time."

"The bus driver is injured but he is able to speak," he added.

The bus, operated by the charter company World Wide Travel, was headed to Manhattan's Chinatown neighbourhood with a full load of passengers returning from the Mohegan Sun casino in Connecticut.

World Wide Tours said it in a statement that the company was "heartbroken."

"We are a family owned company and realize words cannot begin to express our sorrow to the families of those who lost their lives or were injured in this tragic accident. Our thoughts and prayers are with them," it said.

According to The New York Times, World Wide Tours was recently flagged by U.S. regulators for troubles with fatigued drivers. The company's buses were involved in two crashes in the past two years that resulted in passenger injuries.

With files from The Associated Press