Boris Johnson will warn ministers coronavirus presents a "significant challenge" at an emergency Cobra meeting on Monday as the number of UK cases soared, including a "family cluster".
The prime minister will finalise the government's new battle plan to tackle the spread of COVID-19 following a weekend in which the number of infected people climbed to 36, with cases now in all four UK countries.
Mr Johnson has faced criticism for waiting until Monday to chair the meeting in which he will lay out coronavirus contingency plans that could include banning public gatherings.
"The number of coronavirus cases around the world is rising every day - and the UK is no exception," he is set to tell the meeting.
"There now seems little doubt that it will present a significant challenge for our country.
"But we are well prepared, and the government and the NHS will stop at nothing to fight this virus."
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Senior ministers, chief medical officer Professor Chris Whitty and chief scientific adviser Sir Patrick Vallance will all attend the Cobra meeting.
First Minister Nicola Sturgeon is also expected to be there after a person from Tayside, near Dundee - who had recently returned from Italy - was diagnosed with COVID-19 on Sunday.
Another 12 cases were also confirmed in England, making it the largest jump in cases the UK has seen in one day.
Three of the 12 are adults related to a man from Haslemere, Surrey, who tested positive on Friday - becoming the first person to be infected within the UK.
Dr James Mapstone, acting regional director for the south of England for Public Health England (PHE), said: "PHE is providing specialist advice to local authority partners around two confirmed cases in Surrey and two in West Sussex.
"The four cases are part of an adult family cluster. We are aware of the people they have been in contact with and we are making contact with those people to issue appropriate advice and steps to take if they start to feel unwell."
Another new patient, from Essex, had also not recently travelled to an infected area, Prof Whitty said.
He added that investigations are ongoing into whether the patient had contracted it "directly or indirectly" from someone who had recently travelled abroad.
One of the 12 patients is from Bury, Greater Manchester and was infected in Italy.
Three of the cases were in West Yorkshire, including two from Leeds who became infected in Iran, while one is from Bradford who had been in Italy.
Two of the new patients are from Hertfordshire, one is from London and the other is from Gloucestershire and linked to a member of staff at St Mary's Primary School in Tetbury, who was identified on Saturday after returning from northern Italy.
A staff member at Willow Bank Infant School in Berkshire was confirmed to have tested positive on Saturday.
On Sunday, the Department of Health announced every department will have a ministerial lead on the virus and a "war room" is being set up to roll out an enhanced public information campaign.
Emergency powers designed to restrict COVID-19 if it becomes endemic, due to be announced this week, would only be "temporary", said Health Secretary Matt Hancock.
He confirmed that "population distancing measures", such as banning public gatherings and cancelling football matches, could be considered by the government, while closing schools may be "necessary".
The Foreign Office confirmed that non-essential staff, as well as dependants, are to be pulled out of the British Embassy in Tehran.
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