More than 200 Israelis died in a surprise large-scale attack by the Palestinian militant group Hamas on Saturday, the army said, as Prime Minister Benjamin Netanyahu vowed to reduce the group's Gaza hideouts to "rubble".

Intense air strikes on the coastal enclave brought the Palestinian death toll to at least 232, Gaza officials said, following Hamas's massive rocket barrage and ground, air and sea offensive, in the conflict's bloodiest escalation in decades.

Gun battles raged into the night between Israeli forces and hundreds of Hamas fighters in at least 22 Israel locations, including at least two where gunmen were holding hostages, the army said.

"Terrorists rampaged and broke into homes, massacring civilians," the army said, adding that more than 1,000 people in Israel were wounded by gunshots or the more than 3,000 incoming rockets.

"We are at war," Netanyahu told the stunned nation in the morning after Hamas had launched its multipronged attack at dawn, half a century after the outbreak of the 1973 Arab-Israeli war.

"I'm telling the people of Gaza: get out of there now because we're about to act everywhere with all our force," the premier said later. "We'll strike them to the bitter end and avenge with force this black day they brought on Israel and its people."

He warned that "all the places in which Hamas is based, in this city of evil, all the places Hamas is hiding in, acting from — we'll turn them into rubble."

"What happened today is unprecedented in Israel and I will see to it that it does not happen again."

As the UN Security Council called an emergency meeting for Sunday, President Joe Biden voiced "rock solid and unwavering" support for the US ally and warned "against any other party hostile to Israel seeking advantage in this situation".

'So many bodies'

Secretary of State Antony Blinken also spoke to Egypt, a key intermediary between Israel and Hamas about the "urgency in achieving an immediate halt" to the fighting, State Department spokesman Matthew Miller said.