Israeli tanks have advanced into Deir al-Balah in central Gaza for the first time, triggering a fresh wave of displacement among civilians.

Local journalists said tanks entered southern and eastern areas of the city on Monday amid heavy air and artillery strikes, a day after Israel ordered residents in several areas to leave.

Deir al-Balah is one of the few areas of Gaza where Israel has not conducted a major ground operation during its 21-month war with Hamas.

The UK and 24 other nations meanwhile condemned the killing of hundreds of Palestinians at food aid points. “The war in Gaza must end now,” they said. “The suffering of civilians has reached new depths.”

The UN said the evacuation order in Deir al-Balah affected tens of thousands of Palestinians and dealt “another devastating blow” to humanitarian efforts.

The neighbourhoods contain dozens of camps for displaced families as well as aid warehouses, health clinics, and critical water infrastructure.

Local journalists told the BBC that Israeli tanks and other military vehicles pushed into eastern Deir al-Balah on Monday from the direction of the Kissufim crossing and under the cover of heavy artillery and air strikes.

Dozens of shells struck the Abu al-Ajin and Hikr al-Jami areas, they said.

Night-time footage shared on social media showed explosions and the sound of gunfire. Local medics said several people had been killed by shelling.

A spokeswoman for the British charity Medical Aid for Palestinians (MAP), which operates a clinic in Deir al-Balah, described the situation as “extremely critical”.

“Shelling is taking place all around our office, and military vehicles are just 400m away from our colleagues and their families, who endured a harrowing night after relocating there,” Mai Elawawda said in a statement.

On Sunday, the Israeli military ordered the immediate evacuation of six city blocks in southern Deir al-Balah, warning that it would be operating “with great force to destroy the enemy’s capabilities and terrorist infrastructure”.

Leila Ezzat al-Shana and her family – including two young children and her sister-in-law, whose leg has been amputated – told the BBC that she had fled from the Bureij refugee camp, about 5km (2.5 miles) north-east of Deir al-Balah, to the nearby Nuseirat camp on Monday.

“[Bureij] was a really dangerous place,” she said. “We saw the tanks in front of us. There were so many snipers shooting everywhere. The shots entered the home in front of me… It’s a miracle to stay alive.

“People are losing their minds and they are falling to the ground due to the lack of food.”

The UN Office for the Co-ordination of Humanitarian Affairs (OCHA) said on Sunday that hundreds of families had already fled.

It said the evacuation order covered about 5.6 sq km (2.2 sq miles) of Deir al-Balah, home to between 50,000 and 80,000 people, including 30,000 in 57 camps for the displaced.

OCHA said UN staff were remaining in Deir al-Balah, spread across dozens of premises whose co-ordinates had been shared with Israel, and stressed that they must be protected.

The affected areas house several aid warehouses, four primary health clinics, four medical points, a water desalination plant, three water wells, a water reservoir, a solid waste dumping site, and a wastewater pumping station, it added.

“Any damage to this infrastructure will have life-threatening consequences,” it said.

Medical Aid for Palestinians said several humanitarian organisations’ offices and guesthouses had been “ordered to evacuate immediately” by the Israeli military.

Nine clinics including MAP’s Solidarity Polyclinic – which alone cared for around 320 patients a day – had been shut down, it added. Five shelters and a community kitchen had also closed.

The Israel Defense Forces (IDF) said it was maintaining “ongoing and continuous contact” with international aid organisations, to help evacuate “essential institutions”. It did not comment on the military operation.

The UN and other humanitarian agencies relocated key parts of their operations to Deir al-Balah after Israeli ground forces entered the southern city of Rafah more than a year ago.

Israeli sources say that the possible presence of Israeli hostages held by Hamas is one reason why Deir al-Balah had so far escaped the fighting. At least 20 of the 50 hostages still in captivity are believed to be still alive.

Hostages’ families have expressed concern that an offensive could endanger them.

“Can anyone [promise] to us that this decision will not come at the cost of losing our loved ones?” they said on Sunday.

According to the UN, about 87.8% of Gaza is now covered by Israeli evacuation orders or is within Israeli militarized zones, leaving the 2.1 million population squeezed into about 46 sq km of land where essential services have collapsed.

Meanwhile, the World Food Programme warned Gaza’s hunger crisis had “reached new levels of desperation” after more than 100 people were reportedly killed while waiting for food over the weekend.

On Sunday, at least 67 people were killed as they surged toward a convoy of WFP aid lorries near the Zikim crossing point in northern Gaza, according to the Hamas-run health ministry. The Israeli military said its soldiers fired warning shots at a crowd of thousands “to remove an immediate threat”.

“Malnutrition is surging with 90,000 women and children in urgent need of treatment. Nearly one person in three is not eating for days,” the WFP said.

“Only a massive scale-up in food aid distributions can stabilise this spiralling situation.”

In their joint statement, the group of 25 nations including European countries, Canada, Australia, New Zealand and Japan condemned what they said was the “drip feeding of aid and the inhumane killing of civilians, including children”.

“It is horrifying that over 800 Palestinians have been killed while seeking aid.”

It condemned Hamas’s refusal to release all its hostages, and said a “negotiated ceasefire offers the best hope of bringing them home”.

The Israeli foreign ministry said on Sunday that 4,400 lorry loads of humanitarian aid had entered Gaza from Israel since mid-May, when it partially eased a total blockade on deliveries that lasted 11 weeks. Another 700 lorry loads were waiting to be picked up by the UN from the Gaza side of its crossing points, it added.

Israel launched its war in Gaza in retaliation for the Hamas-led attacks on 7 October 2023, which killed about 1,200 people and led to 251 others being taken hostage.

Israeli attacks have since killed at least 58,895 people in Gaza, according to the territory’s health ministry.