A Red Cross-brokered ceasefire has been broken in the Gaza district of Shejaiya after Israeli forces and Palestinian militants continued to fire at one another.

The ceasefire had an agreed two-hour limit to allow rescue workers to reach casualties in the neighbourhood and evacuate the wounded following an intense period of shelling by the Israeli military.

Fighting resumed less than an hour into the truce with the Israeli military claiming that Hamas had breached the ceasefire. Hamas has made no immediate comment on the Israeli claims but reports suggest that both sides continued to fire during the truce.

At least 60 Palestinians were killed by the IDF shelling, according to the Gaza Health Ministry, in what is the heaviest loss of life since the start of "Operation Protective Edge."

The Director of Shifa hospital, Naser Tattar, said that 17 children, 14 women and four elderly civilians were among the 50 people killed while 400 more were wounded. Thousands were evacuated to UN shelters in the centre of Gaza City.

Palestinian Authority President Mahmoud Abbas declared three days of mourning and accused Israel of conducting a massacre.

However, the Israeli military defended their bombardment of the territory, stating that it had sent evacuation warnings to Shejaiya residents two days prior as it sought to target Hamas command centres in the area.

"Two days ago, residents of Shejaiya received recorded messages to evacuate the area in order to protect their lives," an Israeli military spokeswoman said.

Before the attack on the neighbourhood, Gaza's health ministry said that 348 Palestinians had been killed and nearly 3000 wounded by Israel since the start of "Operation Protective Edge". Five Israeli soldiers and two civilians have died since the unrest began.