The London Ambulance Service (LAS) says it has received as many emergency calls in recent weeks as it did during the first wave of the coronavirus pandemic.
It says it has had to rely on the support of extra staff members and volunteers to ease pressure on the service.
An LAS spokesman said demand for the service has risen "sharply" in recent weeks, with up to 8,000 calls a day to the 999 emergency number, compared to 5,500 on a typical busy day.
UK variant: The United Kingdom has identified a new, more contagious coronavirus variant, linked to a recent surge in cases in England. Dozens of countries have banned travel from the UK in an attempt to contain it.
More than 2.29 million cases of coronavirus have been reported in the United Kingdom since the beginning of the pandemic, according to data from Johns Hopkins University, and more than 70,000 people have died.
"Our colleagues in emergency departments are also under pressure receiving our patients as quickly as they can. We are working urgently with NHS partners to reduce any delays," the LAS spokesman added.
According to data from the service, the LAS took 7,918 calls on December 26 this year, in comparison to 5,217 the year before.
"One of our busiest ever days -- 16 March 2020 -- as the first wave of the pandemic peaked, was only marginally busier," an LAS spokesperson told CNN Monday.