The limousine bus Morgan and six others were travelling in overturned in the crash, which happened on the New Jersey Turnpike about 1am local time on Saturday.

Police confirmed Morgan's friend and collaborator James McNair, 63, was killed in the crash. Morgan remains in intensive care at the Robert Wood Johnson University Hospital Centre in New Jersey.

US comedian Tracy Morgan.

A preliminary police investigation found that a Wal-Mart tractor-trailer failed to notice slow-moving traffic and hit the back of the limo bus, which crashed into several other vehicles and overturned near Cranbury Township, NBC News reported.

The driver "failed to observe slow-moving traffic ahead," Sargeant Gregory Williams of New Jersey State Police said. "He observed at the last minute - just prior to impact - the limo bus carrying Morgan and his party."

Kevin Roper, 35, of Jonesboro, Georgia, was later charged with one count of death by auto and four counts of assault by auto, the New York Times reported.

Morgan, 45, rose to fame when he joined the cast of Saturday Night Live in 1996, before starring opposite Tina Fey in the long-running comedy hit 30 Rock. 

"His family is now with him and he is receiving excellent care," said Lewis Kay, Morgan's representative. "We don't anticipate much of a change in his condition today but will provide a further update once more information becomes available."

Morgan's assistant Jeffrey Millea and comedian Ardie Fuqua Jr. also were listed in critical condition, a hospital spokesman, Peter Haigney, said. A fifth passenger, comedian Harris Stanton, was treated and released. Two others were not injured.

In addition to the limo bus and truck, another tractor-trailer, an SUV and two cars also were involved in the accident, which closed the turnpike for more than five hours, AP reported.

Friends and fellow comedians posted messages of support on Twitter.