Britain announced Wednesday it would be closing schools in the coming days to stem the spread of coronavirus, as the death toll topped 100 and Londoners braced for tougher measures to tackle the outbreak.

Prime Minister Boris Johnson had held off following the lead of other European countries in shutting schools, because of the impact it would have on the workforce.

But as the outbreak spreads and the death toll reached 104, up from 71 in a day, he said schools would be closed indefinitely later this week. "After schools shut their gates from Friday afternoon, they will remain closed," he told his daily news conference, without giving a date for their re-opening.

Exceptions will be made for key workers -- including healthcare staff, police and delivery drivers -- and for the most vulnerable children. Johnson earlier this week advised people to work from home and avoid unnecessary social contact and travel, warning the infection rate was starting to spike.

On Wednesday he said this was having an effect but repeated advice for people with symptoms to self-isolate for between one and two weeks, depending on circumstances.  "Everyone must follow the advice to protect themselves and their families, but also, more importantly to protect the wider public," he said.

Johnson added that "we will not hesitate to bring forward further and faster measures." Speculation is rife that London in particular could soon be subject to more draconian measures, as the capital records the most number of cases.

"We know London is ahead of the rest of us so we may see more stringent measures than even those that we have announced so far being taken," Scottish First Minister Nicola Sturgeon said in Edinburgh earlier.

The government will on Thursday introduce legislation giving it emergency powers to deal with the outbreak, including to close premises and restrict gatherings.