LONDON: British Prime Minister Boris Johnson urged people to come forward to have a COVID-19 vaccine on Wednesday, saying the overwhelming majority of people in intensive care in hospital with the disease had not received their booster.

Johnson also said people should celebrate on New Year's Eve cautiously after he decided not to bring in tougher restrictions to limit the spread of the highly transmissible Omicron variant of the virus.

"I'm sorry to say this, but the overwhelming majority of people who are currently ending up in intensive care in our hospitals are people who are not boosted," he told reporters on a visit to a vaccine centre. "I've talked to doctors who say the numbers are running up to 90% of people in intensive care."

"The Omicron variant continues to cause real problems, you're seeing cases rising in hospitals, but it is obviously milder than the Delta variant."