Lewisham and Queen Elizabeth Hospital have restricted visitors to one adult only.
Only one visitor is allowed per patient at a time, while children are not allowed to visit patients at all.
The hospital previously stated that a maximum of two "next-of-kin" were allowed to visit patients at either hospital at one time.
This advice was updated at around 3.20pm.
A spokesperson for Lewisham and Greenwich NHS trust said: "To protect our patients, visiting at both of our hospitals is restricted to one person at a time, and no children.
"Please note this applies to both UHL and QEH.
"We apologise for any inconvenience."
There have been three officially confirmed cases of coronavirus in Lewisham, and one in Greenwich.
Gallions Reach Health Centre announced on Tuesday that one of its patients had tested positive, a day after the first case had been announced by Public Health England.
Specific details about individual cases in Lewisham have not been disclosed.
According to the latest figures, there have been 456 confirmed cases in the UK, and six deaths.
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