By Nidal al-Mughrabi and Maytaal Angel
GAZA/JERUSALEM (Reuters) - At least 19 people were killed in an Israeli air strike on a house near a hospital in north Gaza's Jabalia refugee camp on Wednesday, the enclave's interior ministry said, as thousands of civilians fled southward to avoid fierce Israeli-Hamas ground fighting.
There was no immediate Israeli comment or details from the scene of the reported attack, which if confirmed would be the third on Gaza's largest refugee camp in a week as the war between the Gaza Strip's Islamist Hamas rulers and Israel entered its second month.

Israeli air strikes devastated parts of Jabalia on Oct. 31 and Nov. 1, flattening multi-storey dwellings in a densely populated area of Hamas-ruled Gaza's urban heartland, and Palestinian authorities said at least 195 civilians were killed.
Israel said its air attacks on Jabalia last week killed two Hamas commanders and a number of militants while targeting operational tunnels dug beneath civilian districts.
The air strikes on Jabalia, within Gaza City encircled by Israeli armoured forces, have heightened international alarm at the soaring humanitarian toll of Israel's onslaught into the densely populated coastal enclave.
Israel has blamed Hamas for civilian deaths in Gaza, saying that it is using Gazans as human shields and hiding arms and operations centres in residential areas.

Earlier on Wednesday, thousands of Palestinian civilians trudged in a forlorn exodus out of the north during a four-hour window of opportunity announced by Israel.
The Israeli military has repeatedly told residents to evacuate the north or risk being trapped in the violence.
But the central and southern parts of the small, besieged Palestinian enclave also came under fire again.
Palestinian health officials said an air strike that hit houses in the Nusseirat refugee camp killed 18 people on Wednesday morning. In Khan Younis, six people, including a young girl, were killed in an air strike.

"We were sitting in peace when all of a sudden an F16 air strike landed on a house and blew it up, the entire block, three houses next to each other," said a witness, Mohammed Abu Daqa.
"Civilians, all of them civilians. An old woman, an old man and there are others still missing under the rubble."
The Israeli military said its forces had advanced into the heart of Gaza city, Hamas' main bastion in the territory, while the Islamist group said its fighters had inflicted heavy losses.
Israel struck at Gaza in response to a cross-border Hamas raid on southern Israel on Oct. 7 in which gunmen killed 1,400 people, mostly civilians, and took about 240 hostages, according to Israeli tallies.

Palestinian officials said 10,569 people had been killed of Wednesday, 40% of them children. The level of death and suffering is "hard to fathom", U.N. health agency spokesperson Christian Lindmeier said in Geneva.
TUNNEL NETWORK
Chief Israeli military spokesperson Rear Admiral Daniel Hagari said combat engineers were using explosive devices to destroy a Hamas tunnel network that stretches for hundreds of kilometres (miles) beneath Gaza.
In a statement on Wednesday, the military said it had destroyed 130 tunnel shafts so far. "Combat engineers fighting in Gaza are destroying the enemy's weapons and are locating, exposing and detonating tunnel shafts," it said.

Air strikes had also killed a Hamas weapons maker, Mahsein Abu Zina, and several fighters, the Israeli military said.
Israeli tanks have met heavy resistance from Hamas fighters using the tunnels to stage ambushes, according to sources with the Iran-backed Hamas and separate Islamic Jihad militant groups. Israel says 33 of its soldiers have been killed.
U.N. officials and G7 world powers stepped up appeals for a humanitarian pause in the war to help alleviate the suffering of civilians in Gaza, where whole neighbourhoods have been razed by Israeli bombardment and basic supplies are running out.
"It is ... important to make Israel understand that it is against (its) interests to see every day the terrible image of the dramatic humanitarian needs of the Palestinian people," U.N. Secretary General Antonio Guterres told a Reuters NEXT conference on Wednesday. "That doesn't help Israel in relation to the global public opinion."

Negotiations mediated by Qatar, where several Hamas political leaders are based, are trying to secure the release of 10-15 hostages in exchange for a one- to two-day humanitarian pause in Gaza, a source briefed on the talks said on Wednesday.
FLEEING THE BOMBS
Thousands of Palestinians fleeing from the north wearily made their way in a long line past wrecked and bomb-scarred buildings, witnesses said.
The Israeli military had told them they should move south of the Wadi Gaza wetlands along the main Salah al-Din Road. Huge numbers of displaced people from among Gaza's 2.3 million population are already crammed into schools, hospitals and other sites in the south.

Thousands of others remain inside the encircled north, including at Gaza City's main Al Shifa hospital, where Um Haitham Hejela was sheltering with her young children in an improvised tent.
"The situation is getting worse day after day," she said. "There is no food, no water. When my son goes to pick up water, he queues for three or four hours in the line. They struck bakeries, we don't have bread."
Israel's stated intention is to wipe out Hamas, hammering Gaza from air, land and sea while ground troops have moved in to cleave the narrow coastal strip in two in fierce urban fighting amid the ruins of buildings.
Reuters was unable to verify the battlefield claims of either side.

(Reporting by Nidal al-Mughrabi in Gaza, Maytaal Angel, Emily Rose and Maayan Lubell in Jerusalem, Rami Amichay in Tel Aviv and Matt Spetalnick in Washington; writing by Michael Perry, Angus MacSwan and Mark Heinrich; Editing by Simon Cameron-Moore, Peter Graff, Alex Richardson and Grant McCool)