Dozens of unmarked speedboats pulled into Oman's Khasab port, breaking the dawn silence and marking the start of a wet and treacherous work-day for Iranian smugglers on the Straits of Hormuz.

At least three times a day, the mostly teenage smugglers risk life and limb to carry banned and highly taxed commercial goods on tiny boats from the Omani enclave across the narrow waterway to Iran for sale on the black market.

"It's dangerous but I need the work and the money is good," said an 18-year-old Iranian boat driver, who smuggles everything from flat-screen TVs and microwaves to Indian tea and American soft drinks into Iran.

He had just completed his second trip of the day from the Iranian island of Qeshem, the main receiving port for the smuggled goods. From there, Iranian merchants distribute them to the rest of the country.

The smugglers' route crosses one of the world's most vital shipping lanes, linking the oil-rich Gulf with the Arabian sea and beyond, a path crucial to the world economy as about a fifth of global oil exports pass through it.

It is frequented by US warships and aircraft carriers, Iranian patrol boats, oil-tankers and cargo ships, all of which the smugglers must avoid.

It is also a cause of heightened tensions between Iran and the West since Tehran has threatened to block the waterway in response to increased Western sanctions over its nuclear program.

Despite the risks, the smuggling trade to Iran is thriving, delivering many of the goods prohibited by international sanctions.

"Business slowed down briefly in January when there were a lot of threats going back and forth between Iran and the US," said Zuhair Reza, a 42-year-old Iranian warehouse manager in Khasab, where illicit goods are stored.

"But now, we're back to normal... Business is great. Business is booming," he said.

The drivers meanwhile, who manoeuvre the tiny speedboats packed to the hilt with smuggled commercial goods across the 60-kilometre (40-mile) stretch between Khasab and Qeshem, say the rewards justify the risks that come with the job.

With each round-trip journey, the smugglers, who travel two per boat, pocket about $30 dollars each. But the 40-minute dash across the waterway is rife with danger.

"Sometimes we get shot at by the Iranian patrol boats. Sometimes we get arrested," said another smuggler who lost a friend and co-worker last year when Iranian patrols opened fire on him as he approached Iran's shores.

The weather, however, is their greatest foe.

"We can try to escape from the patrols, or even bribe them if we get caught... but you can't negotiate with the sea," said the Iranian, who asked to remain anonymous.

An Omani customs agent at Khasab's port said some 500 boats make the journey across the Straits daily, a practice he says is legal in the Gulf state, but illegal once the goods cross into Iranian waters.

The agent, who identified himself as Abu Dhahi, said the Omanis inspect and tax the goods before they are cleared for export.

The electronic goods, cosmetics, clothing, tobacco and soft drinks, among a wide range of other products which arrive from neighbouring Dubai, are then loaded onto the speedboats.

As he described the day-to-day operations of the smugglers, young Iranian men loaded boxes of mobile phones, perfumes and hair-removal cream onto waiting speedboats, wrapped them tightly with grey tarpaulin and secured them with rope in preparation for the bumpy ride ahead.

Abu Dhahi said the smugglers are banned from carrying weapons, and all cargo entering and leaving the port is "carefully inspected."

"No weapons, alcohol or drugs are allowed through this port," he said adding that the smugglers do not pose a security threat to the already tense shipping lane.

"These are just young boys trying to make a living," he said. "And as far as we are concerned in Oman, there's nothing illegal going on here."

As dusk set in, the last of the tourist boats dropped off sun-burned tourists, while the local fisherman loaded dead sharks into waiting trucks heading for Dubai's fish market.

Just a few hundred metres (yards) away, the engines of the speedboats roared, and after lining up together as if for a race, the smugglers sped off towards Iran on their last journey of the day.

"By morning I'll be back," said the 18-year-old smuggler. "I'm working seven days a week. I'm saving to get married. Maybe by next year I'll have enough."