Gaza's economy could collapse within weeks unless Israel reopens crucial commercial trade crossings, UN officials and Gazan businessmen warned Wednesday. More than 68,000 workers have lost their jobs since Gaza's borders were closed in mid-June, following fierce factional battles in which Hamas expelled the forces of the rival Fatah faction, said Nasser el-Helu, a prominent Gaza businessman. The closings added to the already high unemployment rate in the narrow coastal strip. Israeli officials say they cannot open the main commercial crossing point at Karni, citing security concerns, though they have promised to maintain the flow of humanitarian aid into Gaza. In recent weeks, some border points were opened to transfer humanitarian supplies. But no industrial material has entered Gaza, bringing construction activity and manufacturing to a halt, including $93 million (â‚¬67.5 million) worth of UN-funded projects employing 121,000 people, according to the United Nations. More than 70 percent of Gaza's factories have stopped production, says Gisha, an Israeli human rights group. The appeal came a day before the so-called Quartet of Mideast mediators, the US, the UN, the European Union and Russia, meet in Portugal with their newly appointed emissary, former British Prime Minister Tony Blair. "We are asking them (the Quartet) to take consideration of what is happening here. They must take political decisions to open all the crossings, and then the operational solutions will be found," said John Ging, director of the United Nations Relief Works Agency in Gaza. The UN provides food aid to 80% of Gaza's 1.4 million people. "Please lift the siege of Gaza," el-Helu said. "Mr. Blair, the siege is destroying our economy, our community." El-Helu said Israeli business partners had begun canceling contracts because Palestinian factories were unable to meet deadlines. He said if the borders remained closed, Gaza's economy would collapse "in one or two weeks maximum."