British police briefly shut London's Westminster bridge and roads close to parliament and the capital's police headquarters on Saturday due to a suspicious vehicle.

A spokesman for the Metropolitan Police said officers had sealed off roads at Victoria Embankment next to the River Thames and close to New Scotland Yard, the head office of the Metropolitan Police, and by Parliament Square.

Images on social media showed a heavy police presence at the central London location that is popular with tourists. The roads were later re-opened.

"The incident in Victoria Embankment has now concluded," police said on Twitter. "The vehicle has been deemed non-suspicious. All roads will now be reopened."

The United Kingdom is on its second-highest level of terrrism alert, after five attacks in 2017 killed a total of 36 people, including one incident on Westminster Bridge.