The smuggling business is booming in Gaza. Each week, cement and weapons are transported through tunnels running under the border between the salient and Egypt, and about 200 cars make the underground journey as well.

Since Israel first imposed its blockade on the Strip, following the capture in 2006 of an Israeli soldier in a cross-border raid, smuggling has become perhaps Gaza's main growth industry, enriching the coffers of the tunnel owners and of the Islamist Hamas movement which administers the Strip.

Israel tightened its blockade in 2007, when Hamas seized sole control of the Strip after routing security personnel loyal to the Palestinian Authority and President Mahmoud Abbas, but if Jerusalem hoped to weaken Hamas, the tactic appears to have backfired, says Ali al-Haik, chairman of the Gaza Employers Association.

Millions of liters of petrol and diesel have made it into the Strip through the tunnels, and Hamas has earned one shekel (around 30 US cents) per liter. Each new car smuggled in is taxed 10,000 dollars by Hamas. The movement nets three shekels (90 US cents) per pack of cigarettes.

Israel has since relaxed the blockade. But weapons and some 19 types of goods - such as certain chemicals, petrol, fertilizer, cement - which Israel fears can be used to make weapons to be used against it by Hamas and other militants, are still not allowed in.

This is how the tunnel owners - one unidentified man in Rafah owns 40 - make their profits. They do so by renting their conduits out. A a small one, 250 meters long, 1.5 meters wide and 1.5 meters high - goes for 4,000 US dollars per month. The renter, Mohammed Mismah, makes his money back by selling the gravel he smuggles in from Egypt.

Former Egyptian President Hosni Mubarak's security forces used to block, damage or destroy the tunnels, he says. That was before the protests which led to Mubarak's ouster. "Now there are no more security forces, we are more relaxed," Mismah laughs happily.

For Mismah, the disadvantage of his tunnel is that the soil is loamy, which means the contraband has to be loaded onto five-meter-long rubber dinghies and dragged through the tunnel. Sandy soil, he says is better, since the dinghies glide along and there is less chance of the boxes containing the goods being jolted and breaking up.

The profits might be easy, but the actual work of digging the tunnels is not. Those who dig the tunnels, such as 26-year-old Akram, work 12-hour shifts, displacing tons of gravel in the dust and heat. It's back-breaking work and pays the equivalent of 8 US dollars per day. "If you give me another job paying 8 dollars a day, I'll take it immediately," Akram says.

But jobs are not easy to come by in the Strip, where the employment rate is 45 per cent, six out of every ten people live below the poverty line, and 70 percent of the Strip's 1.6 million people are dependent on international aid.

About 300 tunnels are estimated to be in continuous operation under the border between the Strip and Egypt. The most elaborate of them are less tunnels than underground roads or even subways.

Some are used to smuggle cars into the enclave and are built in such a way - sloping down at the entrance, in the Sinai, and then sloping up again into the Gaza border town of Rafah - that the vehicle can be driven through. "Without a scratch," laughs Mismeh.

The tunnels no one talks about, at least not loudly, are those used for smuggling weapons. "It's too dangerous," says Mismeh. But one man squats in the sand and sketches a diagram. The weapons tunnels do not run directly from the Sinai to the Strip, but instead emerge in the no-man's land between the two, which is controlled by Hamas. Israel will not bomb them, for fear of hitting Egyptian border posts.

Like his men, tunnel operator Mismeh comes from the Khan Younis refugee camp, where the poorest of the poor live. "Any job is better than this," he says. "But without the tunnels, we would starve."