An Israeli army flare drifts over buildings destroyed during the Israeli ground and air operations in the northern Gaza Strip, as seen from southern Israel on Monday.

Israel has launched its ground incursion into Gaza City, two Israeli officials told CNN early Tuesday.

Israel in August approved a plan to take over and occupy the heavily bombarded city, which it said is one of the last remaining Hamas strongholds.

The incursion began on the outskirts of Gaza City, where the Israeli military has escalated its airstrikes and accelerated its destruction of high-rise towers over the last week. One of the officials said the ground incursion is going to be “phased and gradual” at the beginning.

“Gaza is burning,” Defense Minister Israel Katz wrote on Tuesday. He said the Israel Defense Forces (IDF) was “striking terror infrastructures” and working to secure “the release of the hostages and the defeat of Hamas.”

The ground incursion was supposed to proceed only after the Israeli military forced the evacuation of the densely populated urban area, but only a fraction of the population has left so far.

The United Nations warned last month that Israel’s plans to invade Gaza City would put about 1 million Palestinians who live there at risk of being forcibly displaced. On Monday, an Israeli military official said an estimated 320,000 Palestinians had fled the area so far.

The incursion began with a renewed wave of Israeli strikes, which saw casualties, including children, stream into the enclave’s depleted hospitals. Dozens of injured Palestinians were brought overnight to hospitals near Gaza City, including Al-Shifa Hospital and the Baptist Hospital, according to local officials.

Videos obtained by CNN showed the bodies of multiple bloodied children arriving at hospitals in northern Gaza. Two adults can be seen in one video screaming out in pain as they grieve over the bodies of their children, covered in white shrouds.