By David Jones

NEW BRUNSWICK New Jersey (Reuters) - Actor and comedian Tracy Morgan, best known for his roles on "Saturday Night Live" and "30 Rock," was badly injured early on Saturday when the limo bus he was riding in overturned in a multi-vehicle crash in New Jersey that killed another comic.

Morgan, 45, was in critical condition in an intensive care unit at a hospital in New Brunswick, New Jersey, police and his spokesman said.

The comedian James McNair, also known as Jimmy Mack, was killed in the crash on the New Jersey Turnpike, police said. McNair, who was 63 and lived in Peekskill, New York, was riding in the limo bus with Morgan.

At least three other people were hospitalized following the crash, in which a tractor-trailer struck the back of the limo bus at around 1 a.m. local time near Cranbury Township, New Jersey State Police spokesman Gregory Williams said, citing a preliminary investigation.

After the collision, involving another tractor-trailer, a sport utility vehicle and two other cars, the limo bus was on its side, Williams said.

Morgan was part of a stand-up comedy "Turn it Funny" tour and had performed at a Dover, Delaware, casino on Friday night.

He was taken by helicopter to Robert Wood Johnson University Hospital Center in New Brunswick, Williams said. Morgan's spokesman said the comic would remain there on Saturday.

"His family is now with him and he is receiving excellent care," spokesman Lewis Kay said in a statement. "We don’t anticipate much of a change in his condition today."

Morgan's assistant Jeff Millea and the comedians Ardie Fuqua and Harris Stanton also went to the same hospital. Hospital spokesman Peter Haigney said three of the patients there were in critical condition and one was in fair condition but declined to identify them, citing privacy laws.

The driver of the truck, 35-year-old Kevin Roper, was charged on Saturday with one count of death by auto and four counts of assault by auto, the Middlesex County Prosecutor's Office said, adding that he was expected to surrender to authorities.

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Police were still investigating the crash and the National Transportation Safety Board was also sending investigators.

'STAY STRONG TRACY MORGAN'

Wal-Mart CEO Bill Simon said in a written statement on Saturday that one of the company's trucks had been involved in the crash and said he was praying for the family and friends of McNair and everyone involved.

"We are working quickly to understand what happened and are cooperating fully with law enforcement to aid their investigation," Simon said. “The facts are continuing to unfold. If it’s determined that our truck caused the accident, Walmart will take full responsibility."

Morgan is one of the best-known black comedians in the United States, finding humor in the often fraught realm of American race relations.

Several of his celebrity friends, including comedians George Lopez and Andy Richter and the director Jon Favreau, posted messages of support on Twitter.

"Stay strong Tracy Morgan," the hip-hop mogul Russell Simmons wrote. "We love you."

A few days before his Friday show at Dover Downs Hotel & Casino, a message was posted on Morgan's Twitter account that read: "Dover downs I'm coming with truck loads of funny Delaware stand up get those tix while u can baby!!!!!"

Following that show, Morgan had been due to appear on Saturday in Charlotte, North Carolina.

Morgan shot to fame with roles on "Saturday Night Live" that often poked fun at racial prejudices. One of his best known characters was Uncle Jemima pitching "pure mash liquor" - a sendup of the Aunt Jemima character's maple syrup commercial.

The New York City native spent seven years at SNL before leaving the cast in 2003. He went on to star in the sitcom "30 Rock" for seven seasons alongside Tina Fey and Alec Baldwin. Morgan played an unhinged, reckless comedian called Tracy Jordan in a network television satire that caricatured his SNL days.

"30 Rock" also skewered Morgan's sometimes inflammatory stand-up routine. After reportedly joking during a performance in 2011 that he would stab his own son to death if he spoke in a "gay voice," Morgan publicly apologized.

He has three sons with his first wife, Sabina Morgan, and is now engaged to Megan Wollover, with whom he had a daughter in 2013. Morgan, a diabetic, had a kidney transplant in 2010.

(Additional reporting by Patricia Reaney, Alex Dobuzinskis, Doina Chiacu and Dan Whitcomb; Writing by Jonathan Allen; Editing by Frances Kerry, Gunna Dickson and David Gregorio)