The situation in Gaza City is 'nothing short of cataclysmic', a UN official has told the BBC, as Israeli tanks and troops continue to advance on the third day of a ground offensive.
Olga Cherevko, a spokeswoman for the UN's humanitarian office, said she had seen a constant stream of Palestinians heading south during a recent visit to the city, but that hundreds of thousands remained.
The World Health Organization (WHO) warned that overwhelmed hospitals were on the brink of collapse because it was being prevented from delivering lifesaving supplies.
The Israeli military said its forces were 'dismantling terror infrastructure and eliminating terrorists' in Gaza City.
It has said its objectives are to free the hostages still held by Hamas and defeat up to 3,000 fighters in what it has described as the group's 'main stronghold'.
However, the offensive on Gaza's biggest urban area, where one million people were living and a famine was confirmed last month, has drawn widespread international condemnation.
The UN and its humanitarian partners have recorded at least 200,000 people crossing from northern to southern Gaza since mid-August, when Israel announced its intention to conquer Gaza City. Around 55,000 have made the journey since Sunday.
Cherevko, who works for the UN humanitarian office in the central city of Deir al-Balah, told the BBC she travelled to Gaza City two days ago - a 29km (18 mile) round-trip that took 14 hours.
'The things there, and the scenes on the way to Gaza City, are nothing short of cataclysmic,' she recalled. 'A constant stream of people [are] crossing from the north to the south, many on foot. Inside Gaza City, it's very crowded still because there are hundreds of thousands of civilians still remaining there.'
She said she also witnessed multiple Israeli strikes 'very close' to the UN convoy while in Gaza City, adding: 'It was really just a constant hit after hit while we were there.'
On Thursday morning, witnesses told Reuters news agency they had seen Israeli tanks in the northern Sheikh Radwan neighborhood and the southern neighborhood of Tal al-Hawa, which have come under heavy bombardment in recent days.
The Israeli military said in a statement that its troops were 'expanding' their operations in the city.
At the start of the ground assault on Tuesday, the military's chief of staff, Lt Gen Eyal Zamir, told troops to 'intensify the blows against Hamas and to decisively defeat the Gaza City brigade.' Cherevko warned that many people were unable to comply with the Israeli military's order to evacuate to its designated 'humanitarian area' in the south.
The WHO's chief, Dr. Tedros Adhanom Ghebreyesus, emphasized the urgent need for humanitarian aid, stating that many injured and disabled persons cannot reach safety due to the escalating violence.
Reports indicate that at least 65,141 people have lost their lives since the current hostilities began, highlighting the grave situation facing the civilian populace.
