The actor and comedian Tracy Morgan finished a stand-up comedy show in Delaware on Friday night and headed back to New York City with several other comedians. Around 1 a.m., a tractor-trailer slammed into the back of their luxury van, overturning it and setting off a chain reaction that involved four other vehicles.

When emergency workers arrived, Mr. Morgan was critically injured, and another comedian, James McNair, was pronounced dead at the scene. Two other comedians and Mr. Morgan’s assistant were injured.

Mr. Morgan, 45, a former “Saturday Night Live” and “30 Rock” cast member, and his assistant, Jeff Millea, 36, were airlifted in a helicopter to Robert Wood Johnson University Hospital in New Brunswick, N.J. On Saturday, Mr. Morgan’s publicist said that he remained in critical condition.