Two practices covering almost 17,000 patients, which operate from the County Oak Medical Centre in Brighton, have been closed - along with their branch surgeries.
Calls to the Warmdene Surgery or the Carden Surgery - which share the medical centre in Carden Hill, Brighton are met with a recorded message that directs patients towards NHS 111.
The message says: 'Unfortunately the building has had to close due to an urgent operational health and safety reason.'
On the Warmdene Surgery's website, a message informs patients: 'The practice has been closed for cleaning as a precautionary measure. The practice will be in contact with patients whose appointments have been cancelled and will give guidance on next steps. The practice will be open as usual as soon as possible.'
The BBC reported that the closure came after a staff member at the practice 'tested positive for the coronavirus' - and Public Health England later revealed that of four new UK cases of the virus confirmed on 10 January, two cases 'are healthcare workers'.
At least one report suggested both of the staff were GPs - and the NHS has begun an urgent search for patients and other staff who may have been in close contact.
Update: Two GPs were infected with coronavirus on this holiday.— Chris Smyth (@Smyth_Chris) February 10, 2020
Health officials are trying to trace their patients - but believe they only saw a small number in past two weeks https://t.co/H12PH3rnnn
Public Health England medical director, Yvonne Doyle, said: 'As a result of our contact tracing we now know the new cases announced today are all closely linked to one another. Our priority has been to speak to those who have close and sustained contact with confirmed cases, so we can advise them on what they can do to limit the spread of the virus.
'Two of these new cases are healthcare workers and as soon as they were identified, we advised them to self-isolate in order to keep patient contact to a minimum. We are now working urgently to identify all patients and other healthcare workers who may have come into close contact, and at this stage we believe this to be a relatively small number.
'We would like thank all those who have followed public health advice and have taken the necessary steps to reduce the risk to the general public.'
Brighton and Hove CCG said it was unable to confirm the reason for the practice closures at this stage - but the move comes just days after the CCG reported that a case of novel coronavirus had been identified in Brighton and Hove.
On Friday the CCG said: 'The local NHS have been working closely with Public Health England and our partner organisations to help contain the situation, using robust infection control measures to prevent any possible further spread of the virus. Public Health England are leading on control measures and they are contacting people who may be affected using their established systems for similar situations.
'The local NHS is working around the clock alongside the local Public Health team, Local Authority and partner organisations to manage the situation to ensure our populations remain as safe as possible.'
The GP practice closures in Brighton came on the day government declared the coronavirus outbreak a 'serious and imminent threat' to public health, as the total number of confirmed UK cases rose from four to eight.