Palestinian authorities said a grave site discovered at the Nasser hospital, the main medical facility in central Gaza, contained nearly 400 bodies
Whitty has worked closely with British Prime Minister Boris Johnson, who said earlier on Friday he had been diagnosed with coronavirus.
Britain's Health Secretary Matt Hancock, another top member of the British government's response to the pandemic, also said he had tested positive on Friday, and was self isolating.
Whitty, a 53-year-old consultant physician and epidemiologist, has appeared alongside Johnson at the government's daily briefings on the crisis.
"I will be continuing to advise the government on the medical response to Coronavirus, supported by my deputies," he said on Twitter.