There were no major reports of bombings, artillery strikes or rocket attacks as Israel and Hamas started a four-day ceasefire in Gaza on Friday, the first pause in a 48-day-old war that has devastated the Palestinian enclave.

The truce began at 7 a.m. (0500 GMT), involving a comprehensive ceasefire in north and south Gaza, the release of 13 Israeli women and child hostages by the militants later in the day and aid to flow into the besieged territory. A number of Palestinian prisoners held in Israeli prisons were to be freed in exchange.

A Reuters correspondent near the northern part of Gaza heard no Israeli air force activity overhead, and saw no tell-tale contrails typically left by Palestinian rocket launches.

Lebanon's Al-Mayadeen TV reported that since the start of the truce, no sounds of bombing were heard in Gaza. But it said Israeli forces were preventing residents from returning to their homes in the densely populated northern part of the enclave.

Soldiers opened fire in one incident, Al Jazeera said, but there was no indication that it resulted in casualties.

There was no immediate comment from the Israeli military, which had earlier issued a call on Palestinians to stay away from the northern Gaza Strip, which it described as a "dangerous war zone".

Sirens sounded in two Israeli villages outside the southern Gaza Strip, warning of possible incoming Palestinian rockets. An Israeli government spokesman said Hamas had carried out a rocket launch in violation of the truce but there were no immediate reports of damage.

In Khan Younis town in southern Gaza, where streets were filled with people, Palestinian Khaled Abu Anzah told Reuters: "We are full of hope, optimism, and pride in our resistance. We are proud of our achievements, despite the pain this caused."

Fighting had raged in the hours leading up to the truce, with officials inside the Hamas-ruled enclave saying a hospital in Gaza City was among the targets bombed. Both sides also signalled the pause would be temporary before fighting resumes.

The Indonesian hospital was reeling under relentless bombing, operating without light and filled with bedridden old people and children too weak to be moved, Gaza health officials said. Al-Jazeera quoted Mounir El Barsh, the Gaza health ministry director, as saying a patient, a wounded woman, was killed and three others injured.

Additional aid would start flowing into Gaza and the first hostages, including elderly women, would be freed at 4 pm (1400 GMT), with the total number rising to 50 over the four days, Qatar's foreign ministry spokesperson Majed Al-Ansari said in Doha.

Fuel trucks lined up at the Rafah crossing on the border with Egypt after the truce began, waiting to enter the enclave, television showed.

Egypt has said 130,000 litres of diesel and four trucks of gas will be delivered daily to Gaza when the truce starts, and that 200 trucks of aid would enter Gaza daily.

Palestinians were expected to be released from Israeli jails, the Qatari spokesperson told reporters. "We all hope that this truce will lead to a chance to start a wider work to achieve a permanent truce."

Hamas confirmed on its Telegram channel that all hostilities from its forces would cease.

'Temporary truce'

But Abu Ubaida, spokesperson for Hamas' armed wing, later referred to "this temporary truce" in a video message that called for an "escalation of the confrontation with (Israel) on all resistance fronts", including the Israeli-occupied West Bank where violence has surged since the Gaza war erupted almost seven weeks ago.

Israel's military said its troops would stay behind a ceasefire line inside Gaza, without giving details of its position.

"These will be complicated days and nothing is certain," Israeli military spokesperson Daniel Hagari said.

"Control over northern Gaza is the first step of a long war, and we are preparing for the next stages," he added. Israel had received an initial list of hostages to be freed and was in touch with families, the prime minister's office said.

In an Arabic-language social media post, an Israeli military spokesperson warned Palestinians: "The war is not over yet. The humanitarian pause is temporary. The northern Gaza Strip is a dangerous war zone and it is forbidden to move north. For your safety, you must remain in the humanitarian zone in the south."

Israel launched its devastating invasion of Gaza after gunmen from Hamas burst across the border fence on Oct. 7, killing 1,200 people and seizing about 240 hostages, according to Israeli tallies.

Since then, Israel has rained bombs on the tiny enclave, killing some 14,000 Gazans, around 40 per cent of them children, according to Palestinian health authorities. Hundreds of thousands of Gaza's 2.3 million people have fled their homes to escape the violence, but conditions are becoming more desperate.

Ahead of the ceasefire, fighting became even more intense on Thursday, with Israeli jets hitting more than 300 targets and troops engaged in heavy fighting around Jabalia refugee camp north of Gaza City.

"People are exhausted and are losing hope in humanity," U.N. Palestinian refugee agency UNRWA's Commissioner-General Philippe Lazzarini said on Thursday, having seen "unspeakable suffering" during a visit to Gaza.

"They need respite, they deserve to sleep without being anxious about whether they will make it through the night. This is the bare minimum anyone should be able to have."

International alarm has focused on the fate of hospitals, especially in Gaza's northern half, where all medical facilities have ceased functioning with patients, staff and displaced people trapped inside.

Israel says Hamas fighters use residential and other civilian buildings, including hospitals, as cover - a charge that Hamas denies.