Offensive launched from Gaza represents large failure of Israeli intelligence and is likely to have long-lasting repercussions

• Israel and Hamas at war – live updates

Shocked Israelis woke on the last day of the Jewish high holidays to the wail of sirens as Hamas and Islamic Jihad fired thousands of rockets from Gaza and armed militants broke down the hi-tech barriers surrounding the strip to enter Israel, shooting and taking hostages. Militants in boats also tried to enter Israel by sea.

Palestinians seek refuge but electricity and gas have been cut off and medical infrastructure is on its knees

• Israel and Hamas at war – live updates

Palestinians across the besieged Gaza Strip have described their terror and confusion, as thousands fled a wave of Israeli airstrikes after Hamas’s unprecedented cross-border incursion.

“When we began asking about the situation inside the hospitals we work with, one person described it as a slaughterhouse,” said Mahmoud Shalabi of Medical Aid for Palestinians, who is overseeing support to hospitals across the Gaza Strip.

Israel responds after Palestinian Islamist group launches surprise attack and incursion

• Israel declares state of war after Hamas launches surprise attack – live updates

The Palestinian Islamist group Hamas has launched a surprise attack on Israel, its biggest in years.

Here is what we know so far:

Hamas militants entered Israeli territory in the early hours of Saturday morning, appearing to take control of various communities in the south of the country. Fighting is still going on in some areas.

Hamas fired thousands of rockets towards Israel, according to Israeli authorities. The Hamas military commander, Mohammed Deif, said 5,000 had been fired, but an Israeli military spokesperson said 2,500 had been fired.

The death toll in Israel is at least 40, according to the Israeli national rescue service. The country’s health ministry said at least 561 wounded were being treated in hospital, according to an Associated Press count based on public statements and calls to hospitals.

The Palestinian health ministry says at least 198 people have been killed and 1,610 wounded in Gaza by Israeli retaliation after the Hamas attack.

There are reports of Israeli hostages in Gaza.

“We are at war and we will win it,” the Israeli prime minister, Benjamin Netanyahu, said in a video address to the country.

The British prime minister, Rishi Sunak, said he was “shocked by this morning’s attacks by Hamas terrorists against Israeli citizens”. “Israel has an absolute right to defend itself,” he said.

Adrienne Watson, the spokesperson for the US national security council, said: “The US unequivocally condemns the unprovoked attacks by Hamas terrorists against Israeli civilians. We stand firmly with the government and people of Israel and extend our condolences for the Israeli lives lost in these attacks.”

Saudi Arabia, which has been in talks with the US about normalising relations with Israel, called on both sides to exercise restraint.