There is hardly a Jewish family in the UK which is not affected in one way or another by what has happened in Israel, the chief rabbi has said.
Sir Ephraim Mirvis told OceanNewsUK it was a "time of mourning, of deep grief, and of enormous worry" for the community.
He also warned that "all steps need to be taken in order to guarantee safety".
More than 700 people have been killed in Israel since Hamas launched its attacks on Saturday morning, including 260 at a music festival.
Israel says more than 100 Israelis have also been kidnapped - it is thought most have been taken into Gaza. It has responded by declaring war on the militant group and bombarding Gaza, killing nearly 500 Palestinians.
Speaking to OceanNewsUK , Rabbi Ephraim called it "a traumatic and horrific time", saying there were "many, many people showing their full solidarity with our Jewish community and people in Israel".
"And you know, when we make calls now to other Jewish people in the UK, the first question everybody is asking is: 'How are you? How is your family? Is everybody alright?' Because there is hardly a Jewish family in the UK not affected in one way or another by what has happened."
He continued: "It is important for people to recognise the extent of what is happening, the scale... "Antisemitism is a feature of life right around the globe, and we have just witnessed one of the most awful terrorist outrages in living memory, ever since the conclusion of World War Two.
"And we are of course worried, and all steps need to be taken in order to guarantee safety."
His comments come as the Board of Deputies of British Jews issued a warning about hate crimes, saying "previous conflicts have shown us that we are likely to see an increase in antisemitism here in the UK".
"We are in touch with the government and will be working to ensure the police support the Jewish community at this time. We urge any incidents be reported to the police and CST."
It added: "We stand with Israel as it seeks to restore security and reunite families."
Meanwhile, police patrols have increased across London after videos emerged of what appeared to be people celebrating the Hamas attack on Israel.
The Met Police said it was providing a visible presence to "reassure communities".
And on Sunday, Home Secretary Suella Braverman said she expected the police to "use the full force of the law" against displays of support for Hamas, which the UK proscribes as a terrorist organisation.
She said "there must be zero tolerance for antisemitism or glorification of terrorism on the streets of Britain".
Prime Minister Rishi Sunak said the UK government is working "very closely" with its Israeli counterparts to "establish the status of any British nationals on the ground".
He said the scenes from Israel were "horrifying" and "Hamas and the people who support Hamas are fully responsible for appalling acts of terrorism - call it out for what it is".
