Police have been led on a dangerous pursuit that came to a crashing end on a busy motorway, authorities allege.

A Mazda, believed to have been stolen, was spotted on Eve St in Guildford, Sydney about 10.45am on Tuesday before police tried to flag down the driver.

WATCH THE VIDEO ABOVE: Wild police chase ends in M5 crash

Know the news with the 7NEWS app: Download today

“When it did not stop, a pursuit commenced,” NSW Police said.

Vision filmed by a bystander showed the Mazda being driven on the sidewalk, around where police had set up a roadblock.

Stunned workers said there were police cars “everywhere”.

“They’re just going that way, some of them (were) going that way and some that way,” one person told 7NEWS.

“So we (are) just confused. I don’t know what’s going on.”

A man is under police guard in hospital following after police were led on alleged pursuit. Credit: 7NEWS

The pursuit ended when the vehicle crashed on the M5 at Revesby, near The River Rd, NSW Police said.

A man aged in his 30s was treated by ambulance paramedics and taken to Liverpool Hospital in a stable condition.

He is under police guard and inquiries are ongoing.