Two members of London’s Strictly Orthodox community died at the weekend after contracting coronavirus, the Board of Deputies has confirmed.
Meanwhile, a member of Manchester's Charedi community is also believed to be in intensive care as a result of the virus.
On Monday Board officials are to begin the grim task of contacting communal burial organisations to learn whether other deaths were recorded over the weekend.
Willi Stern, 85, - a Hungarian-born survivor of Belsen who came to Britain as a refugee - and Rina Feldman, 97, were both named as victims of the virus by leaders of their respective communities.
In a separate statement the Board confirmed: "We are aware that two members of the Jewish community sadly lost their lives over the weekend."
Mr Stern, who took control of the private sector landlord group Freshwater in the 1960s, was the subject of national media coverage when his Stern Property Group collapsed in 1974 with debts of around £143m.
He was bankrupted with debts of about £118m and banned again from serving as a company director in 2000.
The deaths came amid concern the Strictly Orthodox community in Stamford Hill was failing to head the repeated warnings to minimise social contact to contain the spread of coronavirus.
On Sunday afternoon, one community organisation drove through streets where many Charedim live broadcasting a message through a loud speaker warning of the dangers of the virus.
At the weekend some synagogues, including those under the major strictly Orthodox umbrella organisation the Union of Orthodox Hebrew Congregations, remained open for Shabbat.
The UOHC said healthy men were fine to attend services, while women, children and men at risk were told to avoid shul.
In a video posted to Twitter by the If You Tickle Us blog about Charedi life, local resident Yitzchok Kornbluh, launched an angry attack on those who had attended shuls that "were full," and who had used mikvaot [ritual baths] which he also said were "full."
He added: “[I] was stopped Friday by someone who genuinely didn’t know whats going on. When I said it’s… real danger, he said, 'But the rabbonim [rabbis] haven’t closed shuls'."
The Board of Deputies are to step up moves to ensure that the Strictly Orthodox communities follow government advice on the pandemic.
A letter was circulated in Stamford Hill, signed by 20 Jewish doctors, that told Charedim their community was "at higher risk".
It reiterated the Government advice about minimising social contact and for anyone who feels symptoms to isolate at home.
"This is a case of pikuach nefesh (saving a life) and we are all responsible," it said.
Chief Rabbi Ephraim Mirvis, head of the United Synagogue, made an unprecedented announcement last week that all synagogues under his authority would be closed in order to protect life and prevent the spread of the virus.
Most communities were saying prayers for members of their congregations who are sick with the virus.
On Sunday night, Rabbi Joseph Dweck said in an online sermon that four people in the "wider" Spanish & Portugese community had died at the weekend.