As coronavirus cases soar in London, Mayor Sadiq Khan has declared a "major incident" and says hospitals are at risk of being overwhelmed.

"The threat this virus poses to our city is at crisis point," Khan said in a statement on Friday.

"The number of cases in London has increased rapidly with more than a third more patients being treated in our hospitals now compared to the peak of the pandemic last April," he added. "The stark reality is that we will run out of beds for patients in the next couple of weeks unless the spread of the virus slows down drastically."

A variant of the virus recently identified in the U.K. is believed to be more transmissible, contributing to the dramatic rise in cases. "In England, the variant went from rare to dominating the outbreak in about three months," as NPR's Michaeleen Doucleff reported.

"One in 30 Londoners now has COVID-19," Khan said. The London Ambulance Service is taking 8,000 calls per day, which the city said is about 2,500 more than a "typical busy day." And nearly 500 people have died in London hospitals because of COVID-19 complications in the past three days.

The city declares a major incident when an event is "beyond the scope of business-as-usual operations, and is likely to involve serious harm, damage, disruption or risk to human life or welfare, essential services, the environment or national security," according to the mayor's statement.

The mayor is taking steps to ramp up coordination for the medical response, and is seeking more financial assistance for city residents who cannot work because of the pandemic.

Londoners are asked to "please stay at home except for absolutely essential shopping and exercise," Georgia Gould, chair of , said in a statement.

England went into its third national lockdown earlier this week, including a strict stay-at-home order.

The U.K. launched a massive vaccination campaign last month, starting with the Pfizer-BioNTech vaccine and later including the AstraZeneca-Oxford vaccine. On Friday, its medicines regulator authorized use of the Moderna vaccine, giving U.K. health care workers a new weapon in their arsenal to try to stop the virus.

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