A health official said a polio vaccination campaign began in Gaza on Saturday, while an aid worker said a large-scale rollout would begin on Sunday, coinciding with a "humanitarian pause" agreed by Israel and Hamas.
The vaccination drive was announced after Gaza recorded its first polio case in a quarter of a century earlier this month.
Local health officials along with the UN and NGOs "are starting today the polio vaccination campaign", Moussa Abed, director of primary health care at the health ministry in Hamas-run Gaza, told AFP on Saturday.
An unspecified number of children received the first dose of the vaccination, which involves two doses and is administered orally, at Nasser Hospital in the southern city of Khan Yunis.
Among them was Amal Shaheen's three-year-old daughter, who was already in the hospital being treated for pneumonia.
"We have been in the hospital for 17 days... I spend all my days worrying about her," Shaheen said.
"Today she was vaccinated against polio to protect her, like all the children in the hospital have been vaccinated."
The World Health Organization (WHO) said on Thursday that Israel had agreed to a series of three-day "humanitarian pauses" in Gaza to facilitate vaccinations, though officials had earlier said the campaign was expected to start on Sunday.
- 'Not a ceasefire' -
An international aid worker told AFP that Palestinian authorities had organised a launch event on Saturday and that the vaccination campaign was still expected to begin in full on Sunday.
COGAT, the Israeli defence ministry body which oversees civilian affairs in the Palestinian territories, said on Saturday that vaccines would be given daily from 6:00 am (0300 GMT) until 2:00 pm for three days in central Gaza, three days in southern Gaza and three days in northern Gaza.
"At the end of each regional vaccination campaign, a situational assessment will be conducted for the area," it said.
The Palestinian health ministry distributed a slightly different schedule, with the vaccine programme lasting four days in each location.
The ministry identified 67 vaccination centres -- mostly hospitals, smaller health centres and schools -- in central Gaza, 59 in southern Gaza and 33 in northern Gaza.
Poliovirus is highly infectious and most often spread through sewage and contaminated water -- an increasingly common problem in Gaza as the Israel-Hamas war drags on.
The media office of the Hamas-run government in Gaza said on Saturday that the vaccination campaign required an "immediate ceasefire".
Israeli Prime Minister Benjamin Netanyahu has said measures to facilitate polio vaccination in Gaza are "not a ceasefire".
The campaign aims to cover more than 640,000 children under 10 years old.
Michael Ryan, WHO deputy director-general, told the UN Security Council this week that 1.26 million doses of the oral vaccine had been delivered in Gaza, with another 400,000 still to arrive
The Ramallah-based Palestinian health ministry said earlier this month that tests in Jordan had confirmed polio in an unvaccinated 10-month-old baby from central Gaza.
Poliovirus is highly infectious and most often spread through sewage and contaminated water -- an increasingly common problem in Gaza as the Israel-Hamas war drags on.
The disease mainly affects children under the age of five. It can cause deformities and paralysis and is potentially fatal.
- '100 percent safe' -
Bakr Deeb told AFP on Saturday that he brought his three children -- all under 10 -- to a vaccination point on Saturday despite some initial doubts about its safety.
"I was hesitant at first and very afraid of the safety of this vaccination," he said.
"After the assurances of its safety, and with all the families going to the vaccination points, I decided to go with my children as well, to protect them."
Abed, the health official, stressed on Saturday that the vaccine was "100 percent safe".
The war in Gaza was triggered by Hamas's unprecedented attack on southern Israel on October 7 which resulted in the deaths of 1,199 people, mostly civilians, according to an AFP tally based on Israeli official figures.
Israel's retaliatory military campaign has killed at least 40,691 people in Gaza, according to the territory's health ministry. The UN rights office says most of the dead are women and children.
Incessant Israeli bombardment has also caused a major humanitarian crisis and devastated the health system.