Airman Spencer Stone, one of three Americans that helped to thwart a terror attack on a French train in August, has been stabbed in Sacramento, California.

Spencer Stone, 25, was attacked while defending a friend, and is currently in a stable condition at a local hospital, an Air Force official said.

Police say the stabbing took place on a Sacramento street corner in the early hours after an argument escalated. No arrests have been made.

They hope to release more information later today.

Spencer Stone two others, Alek Skarlatos and Anthony Sadler, were hailed as heroes for tackling a man who was carrying a Kalashnikov rifle, an automatic pistol with ammunition clips and a box cutter knife.

The men, assisted by other passengers, threw him to the floor of the carriage, removed his guns and restrained him.

Spencer Stone was slashed by the attacker and later required surgery to reattach part of his hand.

The three Americans were hailed by French President Francois Hollande and greeted as heroes upon their return to the US.

They received awards from Secretary of Defense Ashton Carter and met President Barack Obama at the White House.

Investigators said on October 8 they did not expect Spencer Stone to survive the attack in Sacramento and initially treated the crime as a homicide.