The meeting was called to "send a strong message that the international community is fully in favor of an immediate ceasefire," said Enrique Yeves, spokesman for Nicaragua's Miguel d'Escoto Brockmann, the president of the 192-member assembly.
The meeting had initially been scheduled for last week but was postponed after the Security Council voted to call for an immediate truce leading to the withdrawal of Israeli forces from Gaza, Yeves said Wednesday.
The council resolution has been ignored by both Israel and Hamas.
The emergency General Assembly session, requested by Malaysia, Indonesia, Iran, Syria, Venezuela and other nonaligned countries, could run through Friday and lead to a vote on a resolution, he said.
Resolutions of the assembly, unlike those of the powerful 15-member Security Council, are not binding.
Thursday's meeting is likely to hear strong condemnation by several UN member states of the Israeli offensive in Gaza amid growing revulsion at the high civilian death toll in the besieged Palestinian enclave, diplomats said.
Gaza medics say at least 1,070 Palestinians have been killed, including 292 children, and another 5,000 wounded since Israel launched its military assault on Gaza December 27.
Thirteen Israelis have also been killed in combat or by rocket attacks.
Meanwhile, the Non-Aligned Movement (NAM) released a statement here condemning "in the strongest terms Israel's blatant disregard of Security Council resolution 1860 (adopted last week)... and its flagrant defiance of the repeated calls from the international community of a complete cessation of military activities."
Iran, Israel's nemesis, said the Jewish state should be held accountable "for its crimes and for the damages it has incurred on the defenseless Palestinians."
"The Israeli war machine must be stopped from shattering more lives and the Israeli war criminals should be brought to justice for the crimes they have perpetrated and continue to perpetrate," Iran's UN Ambassador Mohammad Khazaee said in a letter addressed to D'Escoto and made public Wednesday.
Meanwhile Ban arrived in Amman on the second leg of his regional tour to push for a ceasefire following talks in Cairo with Egyptian President Hosni Mubarak.
The UN secretary general was due to travel to Israel, the West Bank city of Ramallah, Turkey, Syria, Lebanon and Kuwait, where he is scheduled to attend an Arab League summit on Monday.
A Gaza-based Hamas leader, Salah al-Bardawil said in Cairo that his group did not want changes to the "broad outlines" of the Egyptian plan.
Earlier Spanish Foreign Minister Miguel Angel Moratinos reported in Jerusalem that Hamas accepted an Egyptian-brokered truce plan for Gaza.
"Each party has the right to propose its vision in detail. We have in this framework proposed detailed visions and mechanisms," Bardawil said.
"Egypt will discuss it" with Israel, he noted. "We have no differences with Egypt, which is a mediator, but with the Zionist enemy."