Israeli ground forces are pushing into southern Gaza, after three days of heavy bombardment.
Initial reports from Israeli army radio effectively confirmed Israel has launched a ground operation to the north of Khan Younis.
The BBC has also verified images of an Israeli tank operating near the city.
The head of the Israel Defense Forces (IDF) later told troops the IDF was also fighting “strongly and thoroughly” in south Gaza.
Lt General Herzi Halevi was speaking to reservists from the Gaza division about military objectives and the IDF’s killing of Hamas commanders.
He told the soldiers: “We fought strongly and thoroughly in the northern Gaza Strip, and we are also doing it now in the southern Gaza Strip”.
An IDF spokesman later confirmed Israel “continues to expand the ground incursion” across all of Gaza, including troops “conducting face to face battles with terrorists”.
Since a week-long ceasefire ended on Friday, Israel has resumed a large-scale bombing campaign on Gaza, which residents of Khan Younis have described as the heaviest wave of attacks so far.
The seven-day truce saw Hamas release 110 hostages being held in Gaza in return for 240 Palestinians being released from Israeli prisons.
On Sunday morning, the Israeli army issued evacuation orders for several districts of Khan Younis, urging people to leave immediately.
Israeli authorities believe members of the Hamas leadership are hiding in the city, where hundreds of thousands of people have been sheltering after fleeing fighting in the north in the early stages of the war.
A UN official has described a “degree of panic” he has not seen before in a Gaza hospital, after the Israeli military shifted the focus of its offensive to the south.
James Elder, from the children’s agency Unicef, described Nasser Medical Hospital in Khan Younis as a “warzone”.
An adviser to Israel’s prime minister said Israel is making “maximum effort” to avoid killing civilians.
Mr Elder told the BBC he could hear constant large explosions close to the Nasser hospital and children were arriving with head injuries, terrible burns, and shrapnel from recent blasts.
“It’s a hospital I’ve gone to regularly and the children know me now, the families know me now. Those same people are grabbing my hand, or grabbing my shirt saying ‘please take us somewhere safe. Where is safe?'”
“They are unfortunately asking a question to which the only answer is there is nowhere safe. And that includes for them, as they know, that hospital,” he said.
The Hamas-run health ministry in Gaza says more than 500 people have been killed since the bombing resumed.
More than 15,500 people have been killed in the strip since the war began, the ministry also said.
(BBC)
