Man with chainsaw and petrol in hospital

A man who allegedly splashed petrol on a policeman remains in a Sydney hospital, with charges expected to be laid over the incident.

Police say the man was trying to cut down a power pole with a chainsaw at Riverstone on Tuesday morning following a conflict with an energy provider.

He then allegedly threw petrol at three officers, leaving one senior officer in hospital with petrol in his eyes.

The policeman was later discharged and a NSW Police spokeswoman said "he's doing well".

Officers say they attempted to subdue the man with capsicum spray and a Taser, but the petrol ignited and the man caught fire.

He has been treated for minor burns and police expect to lay charges on Wednesday.

A nearby resident told AAP the man had his power cut off and retaliated by trying to cut down a power pole with a chainsaw.