Schools across the UK will close from Friday until further notice, the education secretary has announced.
Speaking in the House of Commons, Gavin Williamson also confirmed that exams and assessments would not be held this academic year.
It comes after a further 32 coronavirus-related deaths in England, taking the total number in the UK to 104.
Mr Williamson told MPs: “I want to provide parents, students and staff with the certainty they need.
“After schools shut their gates on Friday afternoon, they will remain closed until further notice.
“This will be for all children, except for those of key workers and children who are most vulnerable.
“The scientific advice shows that the settings are safe for this small number of children attending, but asking others to stay will just go towards helping us slow the spread of this virus.”
Mr Williamson said examples of key workers include NHS staff, police and supermarket delivery drivers.
Schools will also be encouraged to look after key workers’ children and vulnerable children during the upcoming Easter holidays.
The education secretary added nurseries, sixth forms, further education colleges, independent schools and boarding schools were expected to follow the same approach.
Schools will be given the flexibility to provide meals or vouchers to children who are eligible for free school meals, Mr Williamson also announced.
On the cancellation of exams and assessments, the education secretary said he would be working to “ensure that children get the qualifications that they need”.
Health Secretary Matt Hancock said that childcare support would also be available for social care workers.
At a Downing Street news conference, Prime Minister Boris Johnson said the government’s measures aimed at slowing the spread of coronavirus – now including the closure of schools – were already working.
“We believe that the steps we have already taken, together with those I am announcing today, are already slowing the spread of the disease,” he said.
“But we will not hesitate to go further and faster in the days and weeks ahead and we will do whatever it takes so that we beat it together.”
Mr Johnson did not rule out putting London on lockdown, with coronavirus at its most widespread in the capital.
But he described how a “game-changer” test to determine whether an individual has developed antibodies to tackle the coronavirus is “coming down the track”.
The Welsh government said all schools will close for an early Easter break by Friday at the latest, while First Minister Nicola Sturgeon said Scottish schools will also close by the end of the week.
Northern Ireland First Minister Arlene Foster confirmed that schools would be shut on Monday and could be closed until summer in “unprecedented” action.
Kevin Courtney, joint general secretary of the National Education Union, welcomed Mr Williamson’s announcement on Wednesday.
He said: “It is better for this to take place in an ordered way than the chaotic pattern of closures that was developing.
“We also welcome the clarity that SATs, GCSE, AS- and A-Level exams are to be cancelled.
“Now, more than anything else the government needs to concentrate on ensuring that children in food poverty are fed properly – these children are not just those on free school meals.”
Paul Whiteman, general secretary of school leaders’ union NAHT, said: “This is part of the state-wide response to this crisis.
“I know that the education sector wants to do all that it can to support the country.
But he added: “The situation is moving very quickly, and we have more questions than answers at the moment.”
Purnima Tanuku, chief executive of National Day Nurseries Association, described the government’s announcement as “absolutely devastating news”.
She said: “How can the private nursery sector remain sustainable in the face of mass closures and expensive overheads?
“We must have reassurance from government that as well as continuing to pay the early years entitlement funding, they will support the sector in the same way they have promised for other sectors badly affected by this catastrophe.”
Teachers, head teachers and unions had warned that many schools are so short-staffed that they are struggling to remain open.
More than 600,000 people had signed a parliamentary petition calling for schools and colleges to be closed due to the coronavirus pandemic.