Israel's Prime Minister Benjamin Netanyahu and centrist opposition leader Benny Gantz have agreed to form an emergency unity government.

Netanyahu and Gantz, a former defense minister and military chief of staff, agreed to form a "war cabinet" comprising Netanyahu, Gantz, and Defense Minister Yoav Gallant, a joint statement from Gantz's National Unity party said on Wednesday.

Gantz and Netanyahu met privately for some 30 minutes at the Kirya military headquarters in Tel Aviv, and then stayed there to hash out details of the eagerly awaited potential deal, which many observers and politicians expected to be reached much earlier than five days into the war. Benny Gantz, a senior opposition figure and former defense minister, joined the government for the duration of the conflict.

Netanyahu, Gantz, and Yoav Gallant, the defense minister, are forming a "war cabinet" as Israeli troops continued to build in the south of the country in preparation for an expected ground invasion.

In a televised address late on Wednesday, Netanyahu described atrocities that took place during the weekend attack by Hamas militants, who he said shot children in the head, burned people alive, raped women, and beheaded soldiers. "Every Hamas member is a dead man," he said. "We will crush and destroy it."

Gantz told Israeli citizens that the newly formed government was "united" and ready to "wipe this thing called Hamas off the face of the Earth."

Netanyahu's extreme right-wing coalition partners will continue to serve in the government. The country's chief opposition leader, Yair Lapid, was invited to join the new cabinet but did not immediately respond to the offer.

Inside Gaza, the enclave's sole power station ran out of fuel, adding to the looming catastrophe, particularly for hospitals. "Soon all services vital for the survival of the population, including hospitals, will no longer function," said the Mezan center for human rights in Gaza.

Mahmoud Matar, a surgeon in Gaza, said hospitals were "completely overwhelmed with the number of injuries and the number of dead."

He told the BBC: "The smell of death is all around now in Gaza. There is no water, there will be no electricity, and we have very bad network connection. I am currently looking for water to drink."

Joe Biden described the assault on Israel by Hamas as "the deadliest day for Jews since the Holocaust during a round table of Jewish leaders in Washington on Wednesday evening.

The US president said Saturday's attack was "sheer evil" and a "campaign of pure cruelty against the Jewish people."

"Silence is complicity," Biden said. "I refuse to be silent." He said he had spoken again today with Netanyahu and that the US is "surging" additional military assistance to the Israel Defense Forces.

The UN humanitarian agency OCHA described a "mass displacement" in the Gaza Strip, with more than 263,000 people fleeing their homes. It said that number was expected to rise further.

The death toll that began in Saturday's carnage, carried out by Hamas militants and airstrikes on Gaza by Israeli forces, rose again.