Those in the capital have been warned parks will be shut if people do not follow the government's guidelines on social distancing.
This weekend, spring sunshine and the forced closure of pubs, cafes and restaurants has seen London's parks crowded with people.
Police on Sunday prevented traffic from entering Richmond, Bushy and Greenwich parks, with only workers holding a permit allowed to use car parks.
The Royal Parks, which maintains those parks and five of London's other largest open spaces, also posted on Twitter: "After scenes of crowds not #SocialDistancing yesterday we want to urge you again to follow the government's advice and keep a safe distance from others.
"We have a shared responsibility to keep London's parks safe for everyone who needs them.
"We will keep this situation under constant review. If people do not follow social distancing guidelines, we will have no choice but to close the parks."
Hammersmith and Fulham Council have already shut their parks from 7pm on Sunday "until further notice", while Kew Gardens has been shut "as a precaution to limit the spread of coronavirus".
Victoria Park and Columbia Road flower market in east London were also pictured as being full of people on Sunday.
In the UK, coronavirus is estimated to be at its most widespread in London, with one hospital in the capital having already declared a "critical incident" after running out of critical care beds.
London mayor Sadiq Khan on Sunday issued a stark message on Twitter for all those in the capital, telling them "life has changed".
"Do not leave your home unless you have to," he posted on Twitter.
"Stay at home for yourself. Stay at home to save the lives of your loved ones. Stay at home to help our heroic NHS staff.
"Ignore these instructions and people will die."
Mr Khan had earlier told the BBC's Andrew Marr show: "Social interaction leads to the disease spreading, leads to people dying.
"Don't leave your home unless you really, really have to. Work from home, don't use public transport unless it's genuinely essential.
"Look out for your neighbours who are elderly and vulnerable. Do some shopping for them, leave it on their doorstep. Only buy what you need, there's plenty to get around.
"Don't just do it for yourself, do it to stop the disease spreading. Do it for your vulnerable loved ones who will die if you don't, do it for the heroic NHS who need our help.
"These are extraordinary times which need and demand extraordinary measures."