London will move into England’s highest tier of Covid-19 restrictions, the government said on Monday, citing an exponential rise in infection rates as one of the world’s richest cities struggles to contain the disease.

Health secretary Matt Hancock also said more than 1,000 cases of a new variant of the coronavirus had been identified, mainly in southeast England where the variant may be associated with a rapid rise in infection levels.

“Over the last week, we’ve seen very sharp, exponential rises in the virus across London, Kent, parts of Essex and Hertfordshire,” Hancock told the House of Commons in a statement, referring to counties near London.

“We do not know the extent to which this is because of the new variant, but no matter its cause, we have to take swift and decisive action,” he said, announcing that the entire capital and some neighbouring areas would go into “High Alert” level.

Earlier this month, the government implemented a three-tiered system of restrictions in England to try to keep a second wave of the virus under control after a month-long national lockdown.

However London, whose 9 million people and world-leading financial centre make it the engine of the British economy, is currently only in the second highest tier of restrictions.