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As sunny and warm weather sent many outdoors and into parks in London over the weekend, the top health official in the U.K. warned Sunday that officials may go as far banning outdoor exercise if people still "flout the rules" to stop the spread of coronavirus.

Several parks in London were closed after the warmest weekend in six months sent thousands outdoors into parks on Saturday, with many pictured sunbathing and in large groups.

U.K. Health Secretary Matt Hancock said Sunday that sunbathing is against the guidance officials have set out to prevent the further spread of COVID-19 and that people need to follow the rules.

"The vast majority of people are following the public health advice, which is absolutely critical, and staying at home," he told Sky News. "But there are a small minority of people who are still not doing that -- it's quite unbelievable frankly to see that there are some people who are not following the advice."

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Brockwell Park in London was forced to close Sunday after the local council announced that more than 3,000 people had gone there the previous day, many sunbathing and in large groups.

Similar scenes were reported at Primrose Hill in Camden on Saturday when police said they were "disappointed" in how busy the park was.

"We moved on 100+ people who we found with full picnics or blankets sunbathing or catching up with their friends!" police tweeted.

After police said they returned "a short while later," more crowds were discovered.

Hancock told the BBC on Sunday the government would "take action" if more steps are needed to keep large groups from congregating.

"If you don't want us to have to take the step to ban exercise of all forms outside of your own home, then you've got to follow the rules," he said Sunday.

The health secretary said most people are sticking to guidelines and that everyone should drive to "not have a minority spoil it for everybody."

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Restrictions in outdoor activities vary in Europe from country to country.

In Germany and Britain, residents can get out to exercise and walk their dogs, as well as go to the supermarket, the post office and other essential tasks. Yet in Serbia and South Africa, dog walking is not allowed.

Health officials announced an additional 621 deaths from the virus on Sunday in the country. There were at least 41,903 positive cases of COVID-19 in the U.K. and at least 4,934 deaths, according to Johns Hopkins University

In an address to the nation to be televised later Sunday, Queen Elizabeth II made an appeal for people to exercise self-discipline in “an increasingly challenging time," adding the pandemic brings daunting challenges to everybody.

It was only the fourth time since her reign began in 1953 that the 93-year-old queen has given such an address.

“I hope in the years to come everyone will be able to take pride in how they responded to this challenge,” she said in pre-released remarks. “And those who come after us will say that the Britons of this generation were as strong as any.”

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British Prime Minister Boris Johnson as of Friday still had a fever, saying on Twitter he was "feeling better" after testing positive for COVID-19.

"I still have a temperature and so in accordance with government advice, I just continue my self-isolation until that symptom itself goes," he said Friday.

Johnson's infected pregnant fiancee, Carrie Symonds, tweeted she is “on the mend” after a week in bed.

"I haven’t needed to be tested and, after seven days of rest, I feel stronger and I’m on the mend," she said.

The Associated Press contributed to this report.