Updated: 23.35

A gunman has been killed after he shot a state trooper at a Greyhound bus station in the US state of Virginia.

The state trooper is in a critical condition and two others were taken to a hospital with non-life threatening injuries.

Officers were conducting a training exercise when the gunman approached the trooper and shot him in the chest.

State troopers then fired back and killed the gunman.

More to follow.