A video of a cashier in an American diner reacting calmly as he is held at gunpoint in an armed robbery has gone viral.

The incident occurred at a Jimmy John's in Kansas City on Wednesday (26 April).

In the video a man in a blue sweatshirt enters the sandwich shop and stands at the counter. Speaking to the worker on the till, the robber suddenly pulls a handgun from his sweatshirt, points the weapon directly at him and orders him to empty the cash register.

At one point, the gun is pressed to the cashier's head – but he still keeps his cool. Without even flinching, he calmly removes his plastic gloves and takes the money from the till.

With the gun still pointed at his head, he hands the cash over to the robber who then flees.

In a tweet Kansas City Police confirmed they have arrested the suspect with the help of tips from the public. The robber's name has not been released, Mail Online reports.