Another 1,239 Omicron cases have been found in Britain, the biggest daily increase since the variant was detected in the country, taking the total cases detected in Britain to 3,137.

LONDON - Britain's COVID-19 alert level has been raised from Level 3 to Level 4 "in light of the rapid increase in Omicron cases," British chief medical officers said in a joint statement Sunday.

In the statement, the four chief medical officers and the National Health Service (NHS) England national medical director said the emergence of Omicron "adds additional and rapidly increasing risk to the public and healthcare services."

"Early evidence shows that Omicron is spreading much faster than Delta and that vaccine protection against symptomatic disease from Omicron is reduced," said the statement.

The statement suggested people should continue to "take sensible precautions including ventilating rooms, using face coverings, testing regularly and isolating when symptomatic."

Level 4 means the virus is "in general circulation" and "transmission is high and direct COVID-19 pressure on healthcare services is widespread and substantial or rising."

Another 1,239 Omicron cases have been found in Britain, the biggest daily increase since the COVID-19 variant was detected in the country, taking the total cases found in the country to 3,137, the UK health security agency confirmed Sunday.

Britain reported 48,854 new COVID-19 cases, bringing the total in the country to 10,819,515, according to official figures released Sunday. The country also reported a further 52 COVID-related deaths, taking the national death toll to 146,439.

More than 89 percent of people aged 12 and over in Britain have had their first vaccine dose, and over 81 percent have received both, according to the latest figures. Some 40 percent have received their booster jab, or the third dose.