Members of London's Charedi community have been urged to "remain cautious" and report any cases of coronavirus to a hotline.
Notices circulated by a group called Kehilla NW said there had been a "small number of covid cases within the London kehilla [community]".
It said cases of the virus should be reported to the group's covid hotline "at the request of local rabbonim and doctors".
People were reminded to keep a safe distance from others, wash hands regularly and avoid large crowdings.
The hotline remained open to help with shopping and other needs, the notice said.
A second notice, from Hatzola, the Jewish emergency medical service, said there were "a rising number of community members testing positive for covid-19".
One possible reason was "the many recent visitors from areas where the virus is sitll rampant".
While there had been "no new hospitalisations or severe cases, definitive and preventative immediate action needs to be taken now to keep the virus at bay and avoid a second spike."
The Hatzola circular said it had been endorsed by the rabbinate of the Union of Orthodox Hebrew Congregations.
The number of coronavirus cases overall within the Jewish community have dropped in recent weeks, with just one new death recorded by the Board of Deputies over the week ending July 3 - the same number as the previous week.
But the Luvavitch priimary schools in Stamford Hill were closed for two days earlier this week after one girl tested posttive for the virus.
Weddings attended by up to 30 people have been permitted by the government since Saturday - although no Jewish marriages will take place now for three weeks until after the Fast of Tishah b'Av.
Since the weekend, places of worship have also been able to hold services, where there is no cap on numbers, as long as social distancing is maintained.