Boris Johnson issues stay-at-home order, sending UK into coronavirus lockdown

(CNN) -- The UK is banning people from leaving their homes, apart from a few "very limited" reasons, Prime Minister Boris Johnson announced on Monday as he imposed the most stringent restrictions seen in Britain since the end of World War II.

Police will break up public gatherings and fine people flouting rules, Johnson said in a remarkable televised statement on Monday evening, dramatically ramping up the country's response to the growing coronavirus pandemic.

Shops, gyms, and places of worship will all close, and social events including weddings -- but not funerals -- will be postponed.

"From this evening I must give the British people a very simple instruction -- you must stay at home," Johnson said. "Because the critical thing we must do is stop the disease spreading between households."

"People will only be allowed to leave their home for the following very limited purposes," he added, listing four reasons for which citizens can go outside; shopping for basic necessities, doing one form of exercise a day, providing medical services, or going to work if it is absolutely vital.

"That's all -- these are the only reasons you should leave your home. You should not be meeting friends. If your friends ask you to meet, you should say 'No.' You should not be meeting family members who do not live in your home."

"If you don't follow the rules, the police will have the power to enforce them" by breaking up public gatherings and issuing fines, he added.

The restrictions essentially send the UK into lockdown, though they do not go as far some European countries -- notably Italy and Spain -- in terms of enforcement. Johnson said the measures will be reviewed after three weeks, and people will not require paperwork to go outside.

"No Prime Minister wants to enact measures like this. I know the damage that this disruption is doing and will do to people's lives, to their businesses and to their jobs."

The rules come with deaths from the virus accelerating in the country. A further 54 deaths were announced in the past 24 hours, bringing the nation's total to 335.

Earlier in an unprecedented day in the UK, Foreign Secretary Dominic Raab urged all Britons who are on holiday abroad to change their plans and come home while it is still possible.

"If you are on holiday abroad, the time to come home is now while you still can," Raab said. "Around the world, more airlines are suspending flights and more airports are closing, some without any notice."

Johnson said the measures were necessary to keep the UK's health care system, the NHS, from collapsing under pressure.

"Without a huge national effort to halt the growth of this virus, there will come a moment when no health service in the world could possibly cope; because there won't be enough ventilators, enough intensive care beds, enough doctors and nurses," he said.

"To put it simply, if too many people become seriously unwell at one time, the NHS will be unable to handle it -- meaning more people are likely to die, not just from coronavirus but from other illnesses as well."