The Gaza-based Islamists fired thousands of rockets into Israel and used explosives and bulldozers to break through the fence around the blockaded Palestinian enclave.

Using motorbikes, pickup trucks, motorized gliders and speed boats, the militants streamed into Israel, targeting cities including Ashkelon, Ofakim, and Sderot.

The gunmen carried out a massacre at a music festival attended by hundreds of young Israelis and foreigners near Kibbutz Reim, close to Gaza.

Israel said Hamas took around 150 hostages. They include at least 11 Thais, two Mexicans, and an unknown number of Americans and Germans.

How Israel is responding

Israel declared war on Hamas on Sunday.

On Monday, Defence Minister Yoav Gallant ordered a "complete siege" on Gaza, meaning "no electricity, no food, no water, no gas".

The military has massed tens of thousands of troops and heavy armor near Gaza, and called up 300,000 reservists for a campaign it has dubbed "Swords of Iron".

Netanyahu vowed to reduce to "rubble" the Hamas's hideouts in Gaza, an impoverished territory of 2.3 million people hemmed in by an Israeli-Egyptian blockade for more than 15 years.

On Tuesday the army said it had "more or less restored control over the border" with Gaza, a day after announcing it was evacuating communities near the frontier.

Israel further pounded Gaza overnight Monday-Tuesday, with strikes concentrated on Jabalia refugee camp.

Hamas's armed wing, the Ezzedine al-Qassam Brigades, on Monday said Israeli air strikes had killed "four of the enemy's prisoners". AFP was unable to verify the claim.

On Tuesday, the journalist syndicate in Gaza said four Palestinian journalists were killed by an Israeli air strike.

There have also been two days of clashes between Israeli forces and Hezbollah in the border area between Lebanon and Israel.