A man is in critical condition and five others are in hospital following a serious collision on the Gardiner Expressway early this morning.

It happened shortly after midnight just east of Highway 427.

Police say the 76-year-old driver of an airport limousine was heading eastbound on the highway when he rear-ended a blue Acura, which was heading in the same direction.

"We do not know right now whether the car had slowed or stopped," Sgt. Duncan Miller told CP24 at the scene Tuesday morning.

A 24-year-old man, who was one of four occupants of the Acura, was rushed to hospital in life-threatening condition.

Five other patients were transported to hospital with minor injuries.

The cause of the crash is still under investigation.

“We’ve been investigating most of the night," Miller said.

"We will be conducting a mechanical investigation in conjunction with the reconstruction of the collision that we did tonight."

The eastbound lanes of the highway were closed for several hours between Highway 427 and Kipling Avenue but all lanes reopened shortly before 8:30 a.m.

Police are also investigating information that a third vehicle may have been involved in the collision but fled the scene prior to the arrival of officers.

"We hoped to have that road opened up earlier on but we came to learn through investigating and speaking to witnesses and looking at the scene itself that there appears to be a third vehicle involved. We had to go back to make sure we didn’t miss anything, make sure we collected all the evidence that was possibly there on scene," Sgt. Brett Moore said Tuesday.

"Definitely whenever there is a fail-to-remain, it is a serious incident and we want to make sure we can grab as much evidence at the time."

Police say the vehicle wanted in connection with the incident is believed to be a 2007- 2009 silver Mercedes Benz GL series. The vehicle, police say, will likely have front-end damage.

Police are asking any possible witnesses to come forward and speak to investigators.

"Anybody that was out there, even if you don’t think you saw anything or had anything involved, please give us a call," Moore said.

"Anybody that has a dash camera or anything else, call us at Traffic Services or Crime Stoppers."