Witnesses have described the moment they saw a teenager struck as he tried to cross a motorway to flee from police.

The 19-year-old was attempting to pass the northbound carriageway of the M23 at Crawley when he was struck by a silver Seat Leon at 11.50am on Sunday.

He was airlifted to Royal London Free Hospital in Whitechapel where he remained critically ill last night.

In the 20 minutes before the crash the teenager, from Crawley Down, had been travelling in a stolen car which police were chasing in Moat Road, East Grinstead.

It crashed in London Road, East Grinstead, and police and firefighters were called.

A woman driving the other vehicle involved in the crash was cut free.

But the teenager was driven off in the stolen car, which people said was “smashed up” at this point.

It was dumped in Stace Way, Worth, in Crawley and both the teenager and another man ran off. The second man was arrested shortly afterwards but the teen ran through a field and onto the southbound carriageway of the M23.

Witnesses said he crossed the southbound carriageway safely and “hurdled” over the central reservation - but was hit as he attempted to pass the northbound carriageway.

One driver who witnessed the incident said the woman who struck the teenager was “distraught”.

He said: “I was in the car parallel to the one which hit this guy.

“He came out of the field adjacent to the southbound carriageway, managed to cross to the central reservation, where I thought he would wait before trying to cross the northbound motorway.

“He continued at speed, straight into our path, hit the car beside me and flew up into the air.

“The poor driver who hit him was distraught. She had a young child in the car with her. It must have been horrific.”

Comments were also made on social networking sites.

Laura Beauchamp (COR) said: “I saw him zoom past in a smashed up car and run through the fields by the motorway in Worth.”

Scott Goody added: There was a high speed chase in East Grinstead about 11.30am.

“It resulted in a large crash.”

A Sussex Police spokeswoman said: “Police have referred the incident to the Independent Police Complaints Commission (IPCC) as a matter of standard policy because of the police activity at the time.”

The second man, aged 33 and from Crawley, has been bailed until April 11. He was arrested on suspicion of travelling in a stolen motor vehicle.