An estimated 150,000 Palestinians are being forced to flee areas of central Gaza, the UN has said, as Israeli forces advance on refugee camps there.

Witnesses and Hamas's armed wing reported that tanks had reached the eastern outskirts of Bureij camp.

Israel's military recently expanded its ground offensive to target Bureij and nearby Nuseirat and Maghazi camps.

Israeli bombardment also killed dozens of people across Gaza on Thursday, the Hamas-run health ministry said.

The war was triggered by an unprecedented cross-border attack by Hamas gunmen on southern Israel on 7 October, in which 1,200 people were killed - most of them civilians - and about 240 others taken hostage.

More than 21,300 people have been killed in Gaza - mostly children and women - during 11 weeks of fighting, according to the health ministry.

The IDF has called for the evacuation of a strip of land stretching across central Gaza that includes Bureij and Nuseirat camps, and told the almost 90,000 residents and 61,000 displaced people in the affected areas to move southwards to the town of Deir al-Balah.

However, the UN warned on Thursday that they had nowhere to go because Deir al-Balah is already overcrowded, with several hundred thousand displaced people sheltering there.

Omar, 60, said he had been forced to flee Bureij along with at least 35 members of his family.

"That moment has come, I wished it would never happen, but it seems displacement is a must," he told Reuters by phone. "We are now in a tent in Deir al-Balah because of this brutal Israeli war."

Tom White, Gaza director for UN relief agency UNRWA, said more and more people were being pushed into the southern Gaza town of Rafah, "so more people into a very small strip of land that cannot support them".

On Thursday evening, Gaza's health ministry reported that 20 people had been killed in an Israeli air strike on a building in Rafah that was reportedly housing displaced civilians.

On Thursday morning, the ministry's spokesman announced that 50 people had been killed in Israeli strikes in Maghazi, the northern town of Beit Lahia and in the southern city of Khan Younis.

The deadliest incident was in Beit Lahia, where Palestinian media reported that 30 were killed when a block of four residential buildings was destroyed.

A local TV journalist, Bassel Kheir al-Din, told the Associated Press that 12 members of his family were buried beneath the rubble of one of the buildings and presumed dead, and that nine of their neighbours were missing.

The Palestinian Red Crescent meanwhile said 10 people were killed when Israeli shellfire hit an apartment near al-Amal hospital in Khan Younis, a day after a similar incident in front of the facility reportedly left 31 dead.

The organisation condemned the "intensification in targeting the vicinity" of the hospital, which it runs, and called on the international community to ensure it was protected.

There was no immediate comment from the Israel Defense Forces (IDF), but Khan Younis has been a focus of its ground offensive since the collapse of a week-long truce at the end of last month.

IDF chief spokesman Rear Admiral Daniel Hagari told reporters on Wednesday that the city was "a main Hamas terror centre" and that Israeli forces "continue to operate there using new methods of warfare above and below ground".

He also said troops were fighting in the Bureij area for a third day, adding that they were "eliminating many terrorists and destroying terrorist infrastructure".

Residents told Reuters news agency that the heavy fighting continued on Thursday, with Israeli tanks advancing on the densely populated Bureij camp from the north and east. Hamas's armed wing, the Izzedine al-Qassam Brigades, also posted a video showing what it said was its fighters targeting Israeli soldiers and vehicles in the countryside east of the camp.

In a separate development, the IDF said it "regrets the harm caused to uninvolved civilians" resulting from an air strike in Maghazi on Sunday that killed at least 70 people, according to Gaza's health ministry.

A statement said fighter jets "struck two targets adjacent to which Hamas operatives were located" and that "additional buildings located near the targets were also hit during the strikes, which likely caused unintended harm to additional uninvolved civilians".

Meanwhile in Israel, thousands of teenagers took part in a march to demand a new deal to return the more than 100 hostages still being held by Hamas and other armed groups in Gaza. Many of the demonstrators were from the communities worst affected by the 7 October attacks.

"I'm from Kibbutz Kfar Aza," Shiri Khiyali told the BBC. "I was there on 7 October. My people were kidnapped. We want them back. We want them back now."

Negotiations have reportedly been taking place on another deal that could see more hostages released during a temporary pause in the fighting, after one last month saw 105 hostages freed. However, Hamas has publicly insisted it will only discuss a full ceasefire.

"We are holding contacts at this very moment. I cannot detail the status. We are working to return them all. This is our goal," Prime Minister Benjamin Netanyahu told representatives of the hostages' families at a meeting in Tel Aviv on Thursday.

Separately, there was a new call from UN human rights chief Volker Türk urging Israel to stop what he called "unlawful" killings in the occupied West Bank.

A report said the UN had verified the killing of 300 Palestinians by Israeli forces and settlers in the West Bank since 7 October.

Mr Türk said he was extremely troubled by "the use of military tactics, means and weapons" in law enforcement and "the use of unnecessary or disproportionate force".

A spokeswoman for Israel's prime minister dismissed the report as quite ridiculous and said it belittled the major security threats to Israelis.