A man is recovering in hospital after being hit by a four-tonne truck in Sydney's south-west over a pay dispute.

The man, 31, answered an online ad to work as a labourer for a day, moving furniture from Earlwood to Padstow.

Police say the man completed the job but got into an argument with the truck driver over payment at the end of the day.

The labourer stood in front of the truck and refused to move until he received his money.

It is alleged the driver drove into the man, who fell, became wedged under the engine and was dragged 20 metres along the road.

Police say the truck then stopped, reversed and drove off, leaving the man with serious injuries.

He is receiving treatment at Liverpool hospital for grazing to his back and head, and possible injuries to his lungs and spine.

Bankstown police are urging anyone who knows where the driver is to contact them.