Hospital admissions in England are nearing the level of the first peak, with one ambulance service reporting that Boxing Day was one of its busiest ever days.
There were 21,286 people in hospital with coronavirus in the UK on 22 December, the last day for which government figures are available.
This is only slightly less than the 21,683 patients recorded on 12 April.
The London Ambulance Service said Boxing Day was one of its “busiest ever days”, with 7,918 calls – up by more than 2,500 compared with the same day in 2019.
The numbers were so high that the service was forced to get help from other services across the South.
LAS said: “Like NHS organisations across the country, demand for our services has risen sharply over the past weeks and we are now taking up to 8,000 999 calls a day compared to 5,500 on a typical ‘busy’ day.
“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.”
Saffron Cordery, deputy chief executive of NHS Providers, told the BBC: “We’re seeing a real rise in the pressure for hospital services, but also other types of NHS services as well… ambulance trusts in particular are coming under extreme pressure, as are community and mental health services.”
Regarding London and the South, Ms Cordery added: “Part of the issue is many more people coming through the door with COVID, but also people coming through the door with other conditions as well.”
There are also signs of stress in Wales, as a surgeon there warned that life-saving care for non-COVID patients was under threat if critical care units continued to fill up.
Shakir Mustafa, a consultant surgeon at the Cwm Taf Univeristy Health Board, told Sky News critical care units across South Wales were reaching capacity.
“If it’s filled with COVID patients, it does not mean that we’re just dealing with COVID and not dealing with anything else,” he warned.
“It does mean that we are unable to physically have someone who’s had a bleed after giving birth, for instance – or had a burst appendix, or somebody suffering from sepsis.
“We’d like to look after all our patients and we’re at a situation where this is under threat.”
On Sunday, the government said a further 316 people had died within 28 days of testing positive for COVID-19, bringing the UK total to 70,752.
As of 9am on Sunday, there had been a further 30,051 lab-confirmed coronavirus cases.
However, Scotland is not releasing death figures between 24 and 28 December and Northern Ireland is not releasing case or death figures during the same period.
It comes as more than 24 million people – or 43% of the population – are in England’s highest level of restrictions.
Scotland is also in Level 4 restrictions, a stay-at-home order is also in place across Wales, and Northern Ireland is in a six-week lockdown.