At least 313 Palestinians have been killed as Israel struck 426 targets in Gaza, its military said, flattening residential buildings in giant explosions.

Among those killed in Gaza were 20 children. About 2,000 others are wounded, the Palestinian Ministry of Health said.

The United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) said more than 20,000 Palestinians left Gaza’s border region to head further inside the territory and take refuge in UN schools.

Nebal Farsakh, the spokesperson of the NGO Palestinian Red Crescent Society (PRC), told Al Jazeera that their medical teams were facing “great challenges” in Gaza, adding that they had called on the international humanitarian community to open humanitarian corridors so that NGOs like them could safely carry out their work of helping people in the Gaza Strip.

On Saturday night, Energy Minister Israel Katz said Israel would halt the electricity supply to the besieged territory. The Palestinian enclave – home to some two million people – has been under an Israeli air, land and sea blockade.

Al Jazeera’s Youmna ElSayed said humanitarian conditions in the Gaza Strip were in “constant deterioration”.

What used to be 120 megawatts of electricity has now decreased to only 20MW, provided by power plants that are paid for by the Palestinian Authority, ElSayed said.

Meanwhile, healthcare institutions had to rely on spare generators to continue operating through the night due to Israel’s decision to halt the electricity supply while residents were left to endure the darkness with the unsettling backdrop of explosions not far away.