Israel and Hamas militants are blaming each other, with Palestinian health authorities saying the explosion was caused by an Israeli air strike.
The Israeli military blamed it on a failed rocket launch by a Palestinian militant group.
The blast was the bloodiest single incident in Gaza since Israel launched an unrelenting bombing campaign against the densely populated territory in retaliation for a deadly cross-border Hamas assault on southern Israeli communities on October 7.
The health minister in the Hamas-run government of Gaza, Mai Alkaila, accused Israel of a massacre.
A Gaza civil defence chief said 300 people were killed and a health ministry official said 500 were killed.
Attack on Gaza hospital ‘unprecedented’
The attack on the al-Ahli hospital that killed hundreds was “unprecedented in scale”, the World Health Organization (WHO) said.
There were patients, healthcare workers and internally displaced people in the hospital when it was struck, Ahmed Al-Mandhari, WHO regional director for the eastern Mediterranean, said.
Jordan cancels summit with US President Joe Biden and Egyptian and Palestinian leaders amid claims of strike on Gaza hospital
Jordan has cancelled a summit it was to host in Amman on Wednesday with US President Joe Biden and the Egyptian and Palestinian leaders, amid claims of an Israeli strike on a Gaza hospital that killed hundreds.
Mr Biden was expected to meet the Arab leaders following a solidarity visit to Israel.
Israel has denied responsibility for the hospital blast, and claims the building was hit by a rocket misfired by Palestinian militants.
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Penny Wong describes Gaza hospital explosion aftermath as ‘deeply distressing’
Foreign Affairs Minister Penny Wong has commented directly on the strike on the al-Ahli Hospital in the north of the Gaza Strip, describing the scenes from the explosion as “deeply distressing”.
The scenes from the explosion at a Gaza City hospital are deeply distressing. It is clear there has been a devastating loss of life.
Our thoughts are with those killed, those injured and their loved ones.
— Senator Penny Wong (@SenatorWong) October 17, 2023