Three firms in London have now asked staff to work from home as a precaution against coronavirus.
Oil giant Chevron has asked 300 staff not to come into its office in Canary Wharf “for the time being”.
Crossrail, which shares the same building as Chevron, and media firm OMD, based in central London, have also asked staff to stay away.
The real estate company that manages Canary Wharf suggested the firms had reacted with “an abundance of caution”.
It “strongly encouraged” its tenants to adhere to advice from Public Health England, which says there is no need to send staff home, as most possible cases turn out to be negative.
PHE says even if there is a confirmed case of coronavirus they do not recommend closing the workplace.
In the UK, there have been 7,132 coronavirus tests carried out since the outbreak began to spread beyond China in January.
Of these, 13 were confirmed positive – including four people who returned from the Diamond Princess cruise ship in Japan.
OMD, which is part of Omnicom Media Group, said an employee reported symptoms after returning from Australia with a flight connection through Singapore.
The firm said the chance that it was the coronavirus was minimal but that it was asking staff to work from home “as a precautionary measure, and until definitive results of the employee’s coronavirus test is confirmed”.
Crossrail and OMD did not say how many employees were affected.
Chevron said one of its employees spent the weekend skiing in Italy, a coronavirus hotspot, then returned to work on Monday.
They started feeling unwell and did not go to work on Tuesday. Following NHS advice, the employee reported to hospital to be tested for the infection and is awaiting the results.
The company said it would continue to monitor the situation very closely but in the meantime was taking precautionary measures to reduce its employees’ “risk of exposure”.