The advance came hours before US President Donald Trump is set to present the principles for peace and post-war governance in Gaza at the UN in New York.

Two Australian doctors volunteering at al-Shifa hospital say they are having to carry out operations in filthy conditions with few or no anaesthetics.

Israeli forces are showing no signs of relenting on their new ground offensive in Gaza City as world leaders gather in New York for the United Nations General Assembly and more countries prepare to join the surge of nations recognizing a Palestinian state.

More than half of Gaza City's residents have evacuated the area as Israel Defense Forces continue their offensive in what they call a Hamas stronghold.

As Israel's ground offensive in Gaza City escalates, Shaina Low of the Norwegian Refugee Council warns civilians are trapped, forced to choose between staying under bombardment or fleeing south.

Israeli bombardment over the past 23 months has killed more than 65,000 people in Gaza, destroyed vast areas of the strip and displaced around 90% of the population.

Israeli tanks were stationed on the edge of Gaza City on Wednesday ahead of a planned ground operation into the enclave’s largest urban area, according to eyewitnesses and satellite imagery.

Hamas-linked social media channels say "three collaborators who were spying for the occupation" were executed.

An estimated 1 million Palestinians were living in the Gaza City region before warnings to evacuate began ahead of the offensive. The Israeli military estimates 350,000 people have left the city. The U.N. estimates that more than 238,000 Palestinians have fled northern Gaza over the past month. Hundreds of thousands more have stayed behind.