A man has been arrested after a young woman was sexually assaulted while she slept on a Greyhound bus bound for Ottawa, and charges are expected to be laid.

The incident happened on a Toronto-to-Ottawa bus route at about 9 p.m. as the bus was travelling between Carleton Place and Ottawa.

The victim, a woman in her early 20s, awoke to find the stranger sitting next to her and sexually touching her, said Det. Randy Wagner of the Ottawa police sexual assault unit.

She started screaming and claimed she was being assaulted, leading three men and one woman on the bus to come to her aid, said Wagner.

One of the men informed the bus driver about the alleged incident who then informed security in downtown Ottawa.

Greyhound security guards detained the suspect once the bus arrived in Ottawa and the victim was taken into the care of Greyhound staff until police arrived.

The suspect is a foreign university student studying engineering, police confirmed. He is expected to be charged in the next 24 hours, said Wagner.

Police officers have interviewed one of the men who intervened on the bus and they are hoping to speak to the other two.