Israel levelled a northern Gaza district on Friday after giving families a half-hour warning to escape, and hit an Orthodox Christian church where others had been sheltering, as it made clear that a command to invade Gaza was expected soon.

The Secretary-General of the United Nations visited the crossing between the besieged Gaza Strip and Egypt, and said humanitarian aid must be allowed across as soon as possible.

Israel has vowed to wipe out the Palestinian resistance group Hamas that rules Gaza, after the Oct. 7 incursion of surrounding territories.

"You see Gaza now from a distance, you will soon see it from inside. The command will come," Defense Minister Yoav Gallant told troops gathered at the Gaza border Thursday.

Israel has pounded Gaza with airstrikes and put the enclave's 2.3 million people under a total siege, banning shipments even of food, fuel and medical supplies.

Since Oct. 7, at least 4,137 Palestinians have been killed and 13,000 wounded in Gaza in Israeli strikes since Oct.7, the Palestinian Health Ministry said.

The U.N. says more than a million have been made homeless.

The Orthodox Patriarchate of Jerusalem, the main Palestinian Christian denomination, said Israeli forces had struck the Church of St. Porphyrius in Gaza City, where hundreds of Christians and Muslims had sought sanctuary.

Video from the scene showed a wounded boy being carried from rubble at night. A civil defense worker said two people on upper floors had survived; those on lower floors had been killed and their bodies were still in the rubble.

"They felt they would be safe here. They came from under the bombardment and the destruction, and they said they would be safe here but destruction chased them," a man cried out.

Gaza's media office said 18 Christian Palestinians had been killed. There was no immediate word from the church on the final death toll. It said targeting churches that were used as shelters for people fleeing bombing was "a war crime that cannot be ignored."

Everything destroyed

Israel has already told all civilians to evacuate the northern half of the Gaza Strip, which includes Gaza City. Many people have yet to leave saying they fear losing everything and have nowhere safe to go with southern areas also under attack.

In Zahra, a northern Gaza town, residents said their entire district of some 25 apartment buildings was razed to the ground.

They received Israeli warning messages on their mobile phones at breakfast, followed 10 minutes later by a small drone strike that hammered the message home. After another 20 minutes, F-16 warplanes brought the buildings down in huge explosions and clouds of dust.

"Everything I ever dreamt of and thought that I have achieved was gone. In that apartment was my dream, my memories with my children, and my wife, was the smell of safety and love," Ali, a resident of the district, told Reuters by phone, declining to give his full name for fear of reprisals.

The United Nations humanitarian affairs office said more than 140,000 homes – nearly a third of all homes in Gaza – have been damaged, with nearly 13,000 either destroyed or rendered uninhabitable.

The south of the enclave has also been regularly hit. Rescue workers were combing through the wreckage of a house in the main southern city Khan Younis looking for survivors. One carried the limp body of a child.

"We don’t want to receive aid, we want the destruction and the killing of children in their sleep to stop. We are tired," said neighbour Joumana Khreis.

A man wept while a medic comforted him at the side of a road next to two dead bodies wrapped in white shrouds. The bodies were later held aloft by marchers who carried them through the Khan Younis streets.

Aid still held up

International attention has focused on getting aid to Gaza through the one access point not controlled by Israel, the Rafah crossing to Egypt. U.S. President Joe Biden, who visited Israel on Wednesday, emerged with a promise from Israel to allow limited shipments from Egypt.

U.N. Secretary-General Antonio Guterres toured the checkpoint on the Egypt side and called for a meaningful number of trucks to enter Gaza every day and checks to be quick and pragmatic.

"We are actively engaging with all parties to make sure conditions for delivering aid are lifted," he said.

The conflict is also spreading to two other fronts – the occupied West Bank and the northern border with Lebanon.

The Israeli Defense Ministry ordered residents of the largest town near the Lebanese border, Kiryat Shmona, to evacuate.

Clashes at the border between Israel and Lebanon's Hezbollah movement have been the deadliest since a full-blown war in 2006.

In the West Bank, the Palestinian Health Ministry said 13 people were killed including five children when Israeli troops raided and called in airstrikes on the Nur Shams refugee camp near Tulkarm.

The territory, where Palestinians have limited self rule under Israeli military occupation, has seen the deadliest clashes since the second intifada uprising ended in 2005.