Health workers on the frontline in England will start being tested this weekend to see if they have coronavirus, the government has said.
Tests will be rolled out to critical care doctors and nurses first followed by staff in emergency departments, paramedics and GPs.
It follows criticism from staff over a lack of testing. At present, only very ill patients are being tested.
The British Medical Association (BMA) said the move was "long overdue".
The testing will be on staff with symptoms or on those who live with people that have symptoms.
'Safe to return'
At the daily news conference on the virus epidemic, Cabinet Office minister Michael Gove said antigen testing - which checks whether people currently have the disease - would give health and social care workers "security in the knowledge that they are safe to return to work if their test is negative".
He added: "These tests will be trialled for people on the frontline starting immediately, with hundreds to take place by the end of the weekend - dramatically scaling up next week."
The total number of UK deaths from coronavirus has reached 759, with 14,543 confirmed cases.
Sir Simon Stevens, chief executive of NHS England, said it was "urgently important that we are able to test frontline workers who are off sick or otherwise isolating".
He said that would mean the number of tests carried out doubling by the end of next week.
And he indicated that testing would be widened out to cover more workers, including essential public service workers and social care workers, as capacity increased.
Testing of patients was "vital" and would continue, Sir Simon added.
In Wales, frontline NHS staff are already being screened for the virus.
Three new labs
The first of three new laboratories is expected to start operating over the weekend and will initially process around 800 samples, the government said.
The two other labs are currently being set up and will be opening soon.
This is all being done with the help of universities, research institutes and companies such as Boots, which are lending their testing equipment for use in the labs.
Samples from frontline health workers in coronavirus hotspots like London will be tested first.
The BMA's chairman, Dr Chaand Nagpaul, said the lack of testing so far had been "incredibly frustrating", and it was crucial that testing now be rolled out to all healthcare workers and their households urgently.
"For every healthy member of staff at home self-isolating needlessly when they do not have the virus, the NHS is short of someone who could be providing vital care to patients on the frontline," he said.
Sir Simon said NHS staff were pulling out all the stops to cope with the crisis but he said pressure on the NHS was only going to intensify over the coming weeks.
- 6,200 patients with Covid-19 were currently being treated in hospitals in England
- 33,000 beds were available to treat coronavirus patients
- 18,000 retired doctors and nurses had volunteered to help the NHS