UK Prime Minister Boris Johnson has marked Monday - dubbed "Freedom Day" by some of the local tabloid press - in isolation after coming into contact with the health secretary, who tested positive for COVID-19.

From Monday, there are no limits on how many people can gather and, after more than a year of distancing rules, nightclubs, bars and theatres can fully reopen with no restrictions in England.

Face coverings indoors are recommended but are not mandatory.

London residents welcomed the easing of restrictions even though many said they would remain cautious.

"Being around people will bring more joy to life because everyone has been depressed because of the lockdown," Luisa Edgecombe, who lives in London, said.

"I will still be wearing my mask especially in trains and tubes, and also when in shops, I feel safer wearing it," she added.

"My life probably won't change much, I'll keep my mask on, keep social distance if I have to, keep doing tests if I feel unwell. Freedom day means to me that probably I'll be able to do more stuff, drinking with more friends, that's basically what's going to change really," fellow London resident Charlie Harrison said.

TV footage showed queues of partygoers outside nightclubs just after midnight as youngsters celebrated the change of rules.

But Johnson on Monday warned nightclubs and other venues with large crowds that they must make full vaccination a requirement of entry from the end of September.

On Monday, the UK reported 39,950 new coronavirus cases and 19 deaths in the last 24 hours, according to government data.

Some experts worry that infections could skyrocket to 200,000 a day later in the northern hemisphere summer without restrictions in place.

Iranian authorities on Monday imposed a week-long lockdown on the capital Tehran and the surrounding region as the country struggles with another surge in the coronavirus pandemic.

The lockdown - the country's fifth so far - will begin on Tuesday and last until next Monday.

All bazaars, market places and public offices will close as well as movie theatres, gyms and restaurants in both Tehran province and the neighbouring province of Alborz.

Iran reported 25,441 new cases on Monday and 213 deaths over the past day, bringing the overall death toll to 87,374 from among more than 3.5 million confirmed cases in the pandemic.

Meanwhile, caretaker Dutch Prime Minister Mark Rutte is urging people to work from home again amid a recent spike in infections in the Netherlands.

Dutch infection rates shot up shortly after the government relaxed almost all lockdown measures last month, including allowing nightclubs to reopen.

Rutte subsequently apologised, called the easing an "error of judgment" and ordered nightclubs and discotheques to close again until mid-August.

The seven-day rolling average of daily new cases in Netherlands soared over the past two weeks from fewer than five to nearly 59 new cases per 100,000 people on July 18.

Health Minister Hugo de Jonge says the daily number of new infections appears to be stabilising "but is, of course, too high".

with EFE, PA

Australian Associated Press