Actor Tracy Morgan and two others remained in critical condition Sunday after a chain-reaction wreck that killed a fellow comedian.

The three patients were being treated at Robert Wood Johnson University Hospital in New Jersey on Sunday, hospital spokeswoman Zenaida Mendez said.

The crash early Saturday morning killed James McNair, 63, who was riding in a limo bus with Morgan.

McNair was a comedian who performed under the name Jimmy Mack, said his sister, Valerie Daniel.

"He spoke very highly of Tracy," she said. "They go way back."

Truck driver Kevin Roper, 35, was charged with one count of death by auto and four counts of assault by auto after the tractor-trailer he was driving crashed into the limo bus, a statement from Middlesex County Prosecutor's Office said.

Walmart spokeswoman Brooke Buchanan said the truck driver is an employee.

"This is a tragedy and we are profoundly sorry that one of our trucks was involved," Bill Simon, president and CEO of Walmart U.S., said in a statement.

"The facts are continuing to unfold. If it's determined that our truck caused the accident, Walmart will take full responsibility."

The wreck occurred about 1 a.m. ET on Saturday on the turnpike in Mercer County, Sgt. Gregory Williams of New Jersey State Police said.

"The driver of the tractor-trailer failed to observe slow-moving traffic ahead," Williams said. "At the last minute, he swerved to try and avoid the Mercedes limo bus but struck it from behind, forcing the limo to rotate and overturn."

Four other vehicles were involved in the crash, the prosecutor's office said, but no one in those vehicles was injured.

Williams said he does not believe alcohol played a role in the crash, but that is under investigation.