The United Nations on Tuesday voted to back a resolution that demanded an immediate humanitarian ceasefire in Gaza, coming as U.S. President Joe Biden warned that Israel was losing international support in light of Palestinian civilian casualties.

After dire warnings by UN officials about a growing humanitarian crisis in Gaza, more than three quarters of the 193-member UN General Assembly backed the resolution.

The U.S. and Israel voted against the measure, along with eight other countries.

"A ceasefire means one thing and one thing only. Ensuring the survival of Hamas."

The resolution is not binding.

But it carries political weight, reflecting a global view on the war.

A similar vote was held in the 15-member UN Security Council last week, and vetoed by the United States.

The Palestinian Authority welcomed the resolution and urged countries to pressure Israel to adopt the ceasefire, as fighting between Israel and Hamas intensified across Gaza on Tuesday.

Residents said Israeli shelling in the south was some of the heaviest in days, despite its forces earlier ordering people to flee there for safety.

There are growing signs Israel is becoming diplomatically isolated over its conduct of war.

Biden told a campaign donor event earlier on Tuesday that "most of the world" still backs Israel, but that it was "starting to lose that support by indiscriminate bombing".

Biden's comments came as close ally Australia backed the UN ceasefire resolution, in a rare split with the United States.

A joint statement with Canada and New Zealand said:

"The price of defeating Hamas cannot be the continuous suffering of all Palestinian civilians."

Though they also added that a ceasefire cannot be one-sided, and demanded Hamas stop using Gaza's residents as human shields.