Three teens have been arrested for an early-morning attack on a city bus and two are expected to face charges.

A group of passengers approached a man in his 30s on a bus in Lachine around 4 a.m., police said.

They allegedly asked for money and when he refused he was hit on the head with a blunt object.

"The bus driver immediately stopped the bus," Const. Abdullah Emran said. "The suspects fled the scene."

The incident happened near where Saint-Joseph Boulevard turns into Saint-Jacques Street. 

When police arrived on the scene, they deployed the K-9 unit. The dog tracked down three suspects near where the bus stopped.

All three — aged 17, 18 and 19 — were taken into custody. One has been released without charges. The two others are expected to be charged on Monday with armed assault, obstruction of justice and possession of a weapon.

Police are still looking for a fourth suspect with the help of the K-9 unit. 

The victim was taken to hospital. He's expected to make a full recovery.