A drunk driver who allegedly hit a cyclist in Melbourne's southwest and continued driving has been arrested, police say.

It's believed a 21-year-old man was riding a motorised bicycle in Altona North on Monday afternoon when he was struck by a vehicle.

Police say the driver didn't stop at the scene and continued on until officers found her at a nearby milk bar.

She was taken to Williamstown police station where she returned a breath test reading of 0.137 per cent, police said.

The 31-year-old North Altona woman is due to face Melbourne Magistrates Court on Tuesday on charges including reckless conduct endangering life, and drink driving.

Police said the injured man was taken to hospital to be treated for a possible fractured arm.