Israel hammered Gaza City and its outskirts overnight, residents said on Thursday, after its defence ministry approved an expanded offensive to target the remaining Hamas strongholds in the strip.

The newly approved plan authorises the call-up of roughly 60,000 reservists, deepening fears the campaign will worsen the already catastrophic humanitarian crisis in the Palestinian territory.

"We are not waiting," the Israeli military said in a statement. "We have begun the preliminary actions, and already now, IDF [army] troops are holding the outskirts of Gaza City."

Israel's plans to expand the fighting and take control of Gaza City have sparked an international outcry as well as domestic opposition.

Ahead of the offensive, the Israeli military said the call-up of the reservists would begin in early September.

Gaza City residents described relentless bombardments overnight.

"The house shakes with us all night long – the sound of explosions, artillery, warplanes, ambulances, and cries for help is killing us," one of them, Ahmad al-Shanti, said.

"The sound is getting closer, but where would we go?".

Another resident, Amal Abdel-Aal, said she watched the heavy strikes on the area, a week after being displaced from her home in Gaza City's Al-Sabra neighbourhood.

"No one in Gaza has slept – not last night, not for a week. The artillery and air strikes in the east never stop. The sky flashes all night long," she added.

Gaza civil defence agency spokesman Mahmud Bassal said air strikes and artillery fire overnight targeted areas to the northwest and southeast of Gaza City.

Late on Thursday, the Israeli military detailed a range of operations across the Gaza Strip in recent weeks.

It said the manoeuvres and strikes "created the conditions" for the military to intensify pressure on Hamas and lay the groundwork for the next stages of the campaign.

As Israel tightened its grip on the outskirts of Gaza City, mediators continued to wait for an official Israeli reaction to their latest ceasefire proposal that Hamas accepted earlier this week. (AFP)