At the largest crossing point between Israel and the sealed-off Gaza Strip, capable of processing 200 lorries a day, only one vehicle can be seen. Instead of unloading its cargo of soya inside the border facility, the driver dumps it on a conveyor belt normally used to transfer gravel and cement.

The belt runs more than 200 metres across Karni’s deserted parking lot, over the border fence and into Gaza, where Palestinian merchants reload it into lorries. No Israeli sets eyes on a Palestinian in the process. On such narrow lifelines – there are five crossing points from Israel – hangs the survival of Gaza’s 1.4 million people.

The movement of goods into Gaza had been intermittent at best since Hamas won Palestinian elections early last year. After the Islamist movement drove out its secular Fatah rivals in fighting a month ago, it has been reduced to a trickle.

Aid groups give warning that while Gaza’s basic needs are being met, the narrow coastal belt is facing meltdown if more is not done to open up its borders. At Sufa crossing, to the south, there is more activity but no more contact between the two sides. All morning Israeli lorries drive into a fenced-off field on the border, kicking up clouds of dust as soldiers in guard towers watch for snipers. In the afternoon they withdraw, lock the gates and the field fills with Gaza’s merchants, who load the goods and head back to their hungry towns.

No one stays after dark at what is effectively an airlock between two alienated peoples – except for Israeli soldiers and Palestinian militants. “Until three, it’s the Israelis in there, then they leave and the Palestinians move in. By 7pm it’s empty, then the shooting starts. They start shooting, we start shooting. It’s war,” shrugged Mikha Laufer, the Israeli manager of Sufa.

Israel refuses to deal with Hamas, whose charter denies the Jewish state’s right to exist. Israeli officials say that in any case there is no one to deal with, since Customs administration was dealt with by officials from Fatah, who fled during the battle. Fatah leaders refuse to negotiate with Hamas and have ordered their customs officials not to return to work.

With no Palestinian security forces that Israel can trust, it has banned all exports from the Gaza Strip for fear that Hamas could hide bombs in consignments.

The United Nations has suspended vital construction projects such as homes, schools and sewage treatment in Gaza. “Some $93 million [£46 million] of projects are on hold because cement and other building supplies have run out,” said John Ging, the director of the UNRWA agency providing aid to the Palestinian territories. The UN agency’s construction projects employ 121,000 people in a territory where about 80 per cent of people live on $2 a day.

According to the Israeli advocacy group Gisha, which lobbies for Palestinian rights, Gaza’s economy is being erased rapidly, with 75 per cent of its factories closed because of a lack of raw materials. Gisha said that almost 66,000 people had been laid off, noting that those breadwinners support hundreds of thousands of dependents.

Sari Basha, the director of Gisha, said that Israel’s isolation of Gaza was unlikely to unseat Hamas, which has already won the support of many Gazans for ending a period of law-lessness and cracking down on criminal clans. “Turning people into charity dependents only helps extremist elements,” said Ms Basha.

Major Peter Lerner, of the Israeli Coordination and Liaison Administration, shrugs off such criticism. “Israel has said, since Hamas was elected, there are conditions, and if those are met the barriers can be removed.” Those conditions range from releasing Gilad Schalit, the Israeli corporal kidnapped by Hamas, to ending violence and recognition of Israel.