Local and mayoral elections in England will be postponed for a year to May 2021 due to the coronavirus outbreak.
Downing Street said it would be impractical to hold the elections as planned, as they would come during the peak of the spread of the virus.
Polls were due in 118 English councils, the London Assembly and for seven English regional mayors.
Voting was also due to take place for the London mayor and police and crime commissioners in England and Wales.
It comes after the Electoral Commission said on Thursday the elections should be delayed until the autumn to "mitigate" the impact of the virus.
Meanwhile, visitor access to Parliament will be restricted from Monday, and MPs and peers are being "strongly" discouraged from making overseas trips.
Commons Speaker Lindsay Hoyle said the "proportionate and reasonable" measures would help preserve the operation of Parliament during the outbreak.
Ten people have died with the virus, with 798 cases confirmed UK-wide.
The Cabinet Office said it would be bringing forward legislation to enact the elections delay in England, and would ensure the Welsh authorities had the same powers.
The last time elections were delayed was in 2001, when they took place one month late due to the foot and mouth outbreak.
Acting Liberal Democrat leader Sir Ed Davey said the move to delay the polls was the "right decision".
But he added it was "not clear" why the government had opted for a year-long delay, rather than postpone until the autumn as the Electoral Commission recommended.
Before the postponement was announced, Labour had backed calls for a delay, adding it had "serious concerns" about the welfare of party staff and members.
Labour General Secretary Jennie Formby wrote to local party branches earlier on Friday advising them to suspend campaigning ahead of the polls.
Defending the decision to delay the polls, Justice Secretary Robert Buckland said it was important "everyone feels confident they are able to take part".
"Respecting the annual cycle of local government, postponing them seems to me in the circumstance to be the right thing to do," he added.
James Jamieson, chairman of the Local Government Association, said: "The LGA has been raising a number of issues with government including the possible impact of coronavirus on local elections. The swift decision is very helpful.
"Councils will now continue to put all of their efforts into supporting their local communities as the nation tackles Covid-19."
The decision to delay the polls was also backed by the Association of Electoral Administrators.
Its chief executive Peter Stanyon said: "This is uncharted territory and our members have been raising significant concerns about the safe delivery of these elections."
Political events delayed
Labour has cancelled the special conference in London at which it was due to announce the result of its leadership election on 4 April.
The party said on Thursday it would instead put on a "scaled-back event" instead.
The Liberal Democrats, Plaid Cymru, the Green Party and Welsh Labour have all cancelled their spring conferences due to the spread of the virus.
The SNP and Scottish Conservatives have also announced their spring conferences will be postponed.
Only one MP, health minister Nadine Dorries, has tested positive for the virus - but an increasing number are self-isolating after either feeling unwell or learning that colleagues they have recently mingled with now have the virus.
Speaking on Friday, Mr Buckland said there was currently "no evidence" to suggest that keeping Parliament open posed a "public health issue in itself".
But he added: "If that evidence and information changes, then we'll have to take appropriate steps."