A man was seriously injured with a slashed throat in a stabbing attack at a London train station, while reportedly shouting "This is for Syria" during the attack.

Britain's Counter-Terrorism Command said it was investigating the incident in which up to three people were stabbed and injured.

"We are treating this as a terrorist incident," CTC leader Commander Richard Walton said in a police statement.

A spokesman for the Metropolitan Police said officers were called to the incident at Leytonstone underground station, east London, at 1905 GMT on Saturday where a suspect was reportedly threatening members of the public with a machete.

He said a taser was discharged by one of the officers at the suspect who was then arrested and taken to an east London hospital, where he remains in custody.

The spokesman stated that witnesses nearby had seen two others with minor injuries.

He did not confirm a Sky News report that the suspect shouted the words: "This is for Syria" and "all of your blood will be spilled" during the attack.

Britain is on its second-highest alert level of "severe," meaning a militant attack is considered highly likely. This is mainly due to the threat the authorities say is posed by Daesh militants in Syria and Iraq and their encouragement of supporters to carry out attacks in their homelands.

British lawmakers approved the bombing of Daesh targets in Syria on Wednesday. Britain's air force has since carried out two bombing raids.