A video showing a man racially abusing an elderly passenger on a Ryanair flight has prompted outrage and an investigation by British police.

The video — now viewed on Facebook more than 4-million times — appears to show a white man in an altercation with a black woman over seating arrangements in their row.

Despite protests from another passenger that the woman was disabled, the man can be heard threatening to push her and calling her an "ugly black bastard" in the three-minute clip.

A cabin crew member and a passenger can be seen intervening in an apparent attempt to calm the man, while another can be heard pleading for staff to move the woman.

Ryanair is under heavy criticism for not removing a white man who verbally abused a black woman from its flight.

The no-frills Irish airline has drawn criticism on social media for failing to eject the abusive passenger from the flight.

"He refused to sit next to the woman because she was black," wrote David Lawrence, the man who filmed the incident, in a caption to the video on Facebook. "Ryanair are accountable for the protection of their customers and they failed!"

"The elderly lady was moved to another seat, while the man was allowed to continue his journey with extra room and on board service," he said.

Lawrence said the video was filmed on flight FR9015 from Barcelona to London Stansted on Friday, October 19.

British police say they understand the incident took place while the plane was on the tarmac at Barcelona airport.

Essex Police, the force with jurisdiction over Stansted Airport, said they were made aware of the incident on Sunday. "Essex Police takes prejudice-based crime seriously and we want all incidents to be reported," a spokesman said.

"We are working closely with Ryanair and the Spanish authorities on the investigation."

Ryanair said in a statement: "We have reported this to the police in Essex and as this is now a police matter, we cannot comment further."