Chelsea fans Paris metro
This picture shows the moment Chelsea fans refused to let a black man enter a tube train.Twitter/Arash Karami

Racist Chelsea fans who shoved a black man off a Paris Metro train have been condemned by Prime Minister David Cameron.

The PM told LBC radio the incident, in which Chelsea fans appear to prevent a black man boarding an underground train accompanied by racist chanting, was "extremely disturbing and very worrying".

"It's obviously potentially a criminal offence and so I'm sure the French police will be looking at it very seriously," he said.

"I know the British police will give every assistance that they can. I'm sure Chelsea will co-operate with that fully. These are very, very serious matters."

Chelsea FC has also threatened to ban those responsible.

A police inquiry is also under way to try to identify those involved in the incident which took place prior to Chelsea's Champion's League tie with Paris Saint-Germain on Tuesday night.

A Scotland Yard spokesman said: "We will examine the footage with a view to seeing if we can apply for football banning orders, preventing people from travelling from future matches.

"We will, of course, assist French authorities to identify the people involved and support them in any action they choose to take.

"At the same time we will be working closely with Chelsea football club."