Greek authorities on Thursday hailed a late-night EU deal slashing the country's huge debt as "historic" but critics warned of new sacrifices lying in store under the watchful eye of Brussels. The Athens stock exchange jumped 4.32 percent in afternoon trade after eurozone leaders agreed to slash Greece's debt of over 350 billion euros ($487 billion) by nearly a third. "The country has signed a very major deal, this is a historic day that can put order in our public finances," government spokesman Elias Mossialos told Mega television. Prime Minister George Papandreou will brief President Carolos Papoulias, hold a cabinet meeting and give a 1500 GMT televised address to the nation on the results of the summit, his office said. Speaking to reporters in Brussels hours earlier, Papandreou said Greece had "escaped the trap of default," which he termed a "question of survival" for the country. But main opposition leader Antonis Samaras said the government was boasting for no reason. The EU deal "proves that the government's policy was wrong," he said in a televised address of his own. "The (debt) 'haircut' will bring the country's debt ratio to 120 percent of output in 2020, which is where it was in 2009," Samaras said. "Those who celebrate about bringing the country back to 2009 in 2020 should get serious ... the government responsible for a shipwreck should not speak of salvation," he said. The deal brokered early Thursday will cut 100 billion euros off Greece's debt mountain thanks to an agreement between the eurozone and private sector creditor banks to take a 50-percent loss on their holdings of Greek government bonds. The deal should help cut the ratio of Greece's debt from 160 percent of gross domestic product (GDP) to 120 percent by 2020, still above the EU limit of 60 percent but much more manageable if the economy can be made to grow again. Papandreou noted that the details would still have to be negotiated and concluded "by the end of the year" to enable Greece to finalise budget plans. Already weakened by the crisis and shut out of the financial markets, not all Greek banks will be able to weather the increased cost smoothly and Papandreou admitted some could pass under temporary state control. "It is very likely that a great part of bank shares will come under Greek state control," he told reporters in Brussels. "After restructuring, these shares will be made available on the market as other countries have done," he said. The prime minister was careful to stress that Greek pension and social insurance funds, already under strain from chronic contribution dodging and rising jobless benefits during a biting recession, would be safe. "The insured and pensioners can be sure about their funds and pensions," he said.