Man flown to hospital after collision on Princes Freeway near Little River checkpoint

A man has been flown to hospital after a serious crash on a freeway in Melbourne's south-west.

Emergency crews were called to the Princes Freeway near the Geelong police checkpoint out of metropolitan Melbourne, following reports a car and a truck collided about two kilometres before the Little River Road exit about 6.30am.

A man in his 20s was airlifted to the Royal Melbourne Hospital in a serious but stable condition with upper body injuries.

Traffic is building on the freeway, with extensive delays heading into Geelong.

The freeway is expected to be closed for up a number of hours.

Investigations are continuing at the scene, but the left lane is open with a reduced speed limit of 40km/h.

Motorists are urged to allow extra time for their essential travel.