A man was taken to hospital after he repeatedly stabbed himself in the head on Wednesday at London's Heathrow airport, police and British media said, triggering panic among passengers.

"Sitting at Fortnum and Mason Heathrow T5 when a man runs past stabbing himself in the head -- security has contained the situation," tweeted passenger Neerav Valiram.

An unnamed passenger quoted in Britain's Guardian newspaper said: "I quite quickly saw a Middle Eastern or north African looking gentleman constantly stabbing the side of his head with a knife and blood all down him."

"He never tried to attack anyone apart from himself so I don't think it was a terrorist attack."

Another passenger quoted by the newspaper, Tamara Lynch, said the man was trying to stab himself in the neck, then opened his jacket to try and stab himself in the chest.

"I couldn't see what he was using but he was really trying to ram it in. There was blood all the way down the side of his face and down his shirt," she said.

"My friend got really upset and started crying. There was a poor woman who was lying down on the floor on top of her children trying to protect them."

The Guardian reported that airline employees disarmed the man before airport security, paramedics and police arrived.

A Heathrow spokesman said it was believed the man took the knife from a shop in a departure area of the terminal after security checks and that "it would not have been a really sharp object".

Police said they were called to a shopping area at Heathrow's Terminal 5 at around 1745 GMT.

The man was taken to hospital with non-life threatening injuries, they added.

"It appears that this is a case of self harm. We're not looking for anyone else in connection to the incident," said a police spokeswoman.

London is on high alert after a stabbing attack in a London Underground train station earlier this month that police said was a "terrorist incident". AFP