LONDON (AP) — London and surrounding areas will be placed under the highest level of coronavirus restrictions from Wednesday as infections rise rapidly in the capital, Britain's health secretary said Monday, adding that a new variant of the virus may be to blame for the spread.

Matt Hancock said the government must take swift action after seeing “very sharp, exponential rises” in Greater London and nearby Kent and Essex. He said that in some areas, cases are doubling every seven days.

He told lawmakers that the surge of COVID-19 cases in southern England may be associated with a new variant of coronavirus. He didn’t provide details about the virus variant, but stressed there was nothing to suggest it was more likely to cause serious disease, or that it wouldn’t respond to a vaccine.

“We’ve currently identified over 1,000 cases with this variant predominantly in the south of England although cases have been identified in nearly 60 different local authority areas,” he said. “And numbers are increasing rapidly.”

Hancock said officials are assessing the new strand of the virus, and that the World Health Organization has been notified.

“The medical advice that we have is that it is highly unlikely that this new variant will impinge the vaccine and the impact of the vaccine,” he said.

Under Tier 3 restrictions, the toughest level in England’s three-tier system, people can't socialize indoors and bars, pubs and restaurants must close except for takeout. People are told to minimize traveling within or to the area, and Hancock said people shouldn't take trips into central London to do their Christmas shopping.

In November, London was among areas with the lowest regional infection rates in England. But some areas in and around London have now become virus hot spots.

Local officials in some boroughs of the capital have already advised some schools to close and move to online learning as coronavirus cases spike. On Sunday, Greenwich officials said the borough was experiencing a period of “exponential growth” in cases, with infection rates now at their highest since March.

Mayor Sadiq Kahn has suggested that the government asks all secondary schools and colleges in London to shut early before Christmas because of outbreaks among those ranging in age from 10 to 19.