Heavy fighting between Israeli forces and Hamas trapped thousands of people in Gaza's hospitals on Sunday, as medics and aid workers warned patients will die in the crippled facilities unless there is a pause in the battle.

Bright flares lit up the night sky over Gaza City and blasts echoed across the city, AFP television images showed, as Israel's air and ground campaign to destroy Hamas brought the fight to key medical installations.

"If we do not stop this bloodshed immediately with a ceasefire or at the bare minimum a medical evacuation of patients, these hospitals will become a morgue," medical aid group Doctors Without Borders warned early Sunday.

Al-Shifa hospital in Gaza City, the biggest in the territory, is "totally surrounded and bombardments are going on nearby", the hospital's director, Mohammad Abu Salmiya, said in a statement late on Saturday.

"The medical team cannot work and the bodies, in their dozens, cannot be managed or buried," he said. 

Inside the hospital, Doctors Without Borders surgeon Mohammed Obeid said there was no water, power, food, or internet for about 600 post-operative patients, 37-40 babies and 17 people in intensive care. 

Countless other people are seeking refuge in the hospital grounds.

Two babies died in the Al-Shifa neonatal unit after power to their incubators was cut off and a man also died when his ventilator shut down, the surgeon said in an audio message posted on social media.

"We can see actually the smoke around the hospital. They hit everything around the hospital and they hit the hospital many times," he said.

A sniper had shot four patients within the hospital, he said, with one man hit in the neck and another in the abdomen. People trying to leave the grounds to seek safety further south in Gaza had faced bombardments, the surgeon said.

- Grave concern -

The UN's World Health Organization expressed alarm at the situation in Al-Shifa.

"WHO is gravely concerned about the safety of health workers, hundreds of sick and injured patients, including babies on life support, and displaced people who remain inside the hospital," director-general Tedros Adhanom Ghebreyesus said in a statement.

The Israeli military has denied strikes or a siege at Al-Shifa hospital, and has repeatedly accused Hamas of using medical facilities as command centres and hideouts.

Hames has denied the accusations.

The Israeli army also said it would "provide the assistance needed" to help "babies in the paediatric department to get to a safer hospital" on Sunday, at the request of Al-Shifa staff.

- 'Intense shooting' -

Twenty of Gaza's 36 hospitals are "no longer functioning", according to the UN's humanitarian agency.

The Palestinian Red Crescent Society also called on the international community and humanitarian groups to intervene "immediately and urgently" to protect people in Al-Quds Hospital, also in Gaza City.

Artillery shelling nearby was "causing the building to shake", the Red Crescent said Saturday, reporting "intense shooting at the hospital" where there were about 500 patients and more than 14,000 people seeking shelter.

Infants were facing dehydration because of a lack of breast milk alternatives, it said.

Other hospitals crippled by the fighting include the Indonesian hospital in north Gaza, where the director Atef Al-Kahlot said lack of fuel forced the facility to cut power to their desalination plant, medical scanners and lifts.

"The hospital is working with 30-40 percent of its capacity," Al-Kahlot said.

- Plea for hostages -

Hamas fighters smashed through the militarised border with Israel on October 7, killing around 1,200 people, mostly civilians, and taking about 240 people hostage, according to the most recent Israeli figures.

Israel's campaign in response to wipe out Hamas has killed more than 11,000 people, also mostly civilians and thousands of them children, according to the latest figures from the health ministry in Hamas-run Gaza. 

The ministry has not updated tolls for two days citing the collapse of hospital services.

The families of Israeli hostages spoke of their agony at a rally in Tel Aviv Saturday.

"I came here to shout for my kidnapped parents which are already 35 days not here with us, kidnapped in Gaza. We don't know their situation and we need them to be released immediately," said Yair Mozes, whose parents were both kidnapped from Nir Oz, a kibbutz in southern Israel.

- Exodus -

The intense fighting has accelerated an exodus of people toward Gaza's south.

Tens of thousands of Palestinians are fleeing southwards each day through an evacuation corridor opened by the Israeli military on Friday, according to the UN's humanitarian affairs organisation.

In all, the Israeli army said Saturday that in the last three days around 200,000 Palestinians had left southwards from the area of the northern Gaza Strip where fighting is heaviest.

However, strikes were also hitting buildings at the southern end of Gaza in Rafah, the area of the densely populated territory to which civilians have been urged to evacuate.

"They struck us with a missile, and these are innocent people," said Harb Fojou, standing near the rubble of a destroyed building.

Almost 1.6 million people have been internally displaced since October 7, according to the UN agency for Palestinian refugees UNRWA. This equals about two-thirds of Gaza's population.

- Regional tensions -

The conflict is stoking regional tensions and fears of the war expanding into neighbouring countries.

Israel fighter jets carried out strikes against "terror infrastructure" targets inside Syria in response to cross-border fire directed at the Golan Heights, the military said on Sunday.

Exchanges of cross-border fire have also taken place regularly along the frontier with Lebanon.

Speaking at a summit of Arab and Muslim leaders in the Saudi capital Riyadh, Iranian President Ebrahim Raisi called on Islamic governments to designate Israel's military a "terrorist organisation".

Israeli Defence Minister Yoav Gallant on Saturday warned Iran-backed Hezbollah that launching a war would result in widespread destruction in Lebanon similar to that in Gaza.

"If it (Hezbollah) makes this kind of mistake here, the ones who will pay the price will be first and foremost Lebanese citizens," Gallant told soldiers on Israel's northern border in remarks relayed by his office.

"What we're doing in Gaza, we can also do in Beirut."

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