More than 2,000 NHS frontline staff in England have been tested for coronavirus since the outbreak began, No 10 has confirmed.
Hundreds have been screened since the weekend in a push to get healthy self-isolating medics back to work.
Cabinet minister Michael Gove said a shortage of chemicals needed for the tests meant the NHS – which employs 1.2m in England – could not screen its staff for the virus.
No 10 said test capacity will increase.
The PM’s official spokesman said the government was “working with NHS England, Public Health England and others to ensure that happens”.
It came as the Department of Health confirmed a further 563 patients with coronavirus had died, taking the total number of deaths in UK hospitals to 2,352.