The United Nations human rights chief said the resumption of hostilities between Israel and Hamas in the Gaza Strip on Friday was "catastrophic", with the situation now "beyond crisis point".
"The resumption of hostilities in Gaza is catastrophic. I urge all parties and states with influence over them to redouble efforts, immediately, to ensure a ceasefire -- on humanitarian and human rights grounds," Volker Turk said in a statement.
Israeli warplanes pounded Gaza, sending scores of wounded and dead pouring into hospitals, and rocket sirens blared in southern Israel on Friday.
As the deadline lapsed, Reuters journalists in Khan Younis in southern Gaza saw eastern areas come under intensive bombardment, sending columns of smoke rising into the sky. Residents took to the streets, fleeing for shelter further west and ferrying dead and injured people into hospitals.
In the north of the enclave, previously the main war zone, huge plumes of smoke rose above the ruins, seen from across the fence in Israel. The rattle of gunfire and thud of explosions rang out above the sound of barking dogs.
Barely two hours after the truce expired, Gaza health officials reported that 54 people had already been killed and dozens wounded in air strikes that hit at least eight homes.