The darker your skin - the further down you go: The hierarchical system aboard Italy's migrant boats that governs who lives and who dies

The ruthless human traffickers charging desperate migrants up to £1,300 each to cross the Mediterranean are separating passengers according to race and locking Africans below deck, it has emerged.

More than 1,700 people have died making the perilous voyage in the past week alone and those who survive have told of unimaginable horrors on ships, including starvation, beatings and murders.

Teenagers arriving in the Italian port of Lampedusa told workers from Save the Children how migrants from sub-Saharan African countries were often kept below the deck, deprived of water and sunlight.

A teenage boy from Somalia said he wanted to be called Ali, after his friend who was pushed into the sea alongside other passengers.

“The Libyans who got me to Italy are not human,” he said. “They speak with the gun not with words…they pushed eight Nigerians into the sea.

“And they pushed my friend into the sea. They all drowned.”

Ali survived the trip alongside 400 others, telling how he was crammed below the deck with no windows.

“They didn't give us water otherwise we would have to go to the toilet,” he said.

“There is no toilet on the boat. If you were sick or went up a level to get air the traffickers would shoot you.”

Ibrahim, a 17-year-old boy from Somalia, was also forced below the deck.

“My boat had about 150 people on it,” he said. “The Somalis were put on the bottom level and other nationalities could go on the top level.” He had paid £1,300 for the journey.

Yusuf, a 17-year-old Palestinian boy who reached Italy in February after fleeing Gaza, said he was put on an upper level with other people from the Middle East.

“There were about 250 people in the boat, it had two levels and some Africans were put below,” he added.

“The traffickers had guns and if you talked they said they would throw you overboard or shoot you. They always threatened us with their guns.”

A spokesperson for Save the Children said that many migrants helped by their workers had told similar stories of different races being split up, with the lighter-skinned appearing to receive marginally better treatment.

“What we hear from numerous migrants arriving in Italy is that migrants from African countries are often treated worse than Middle Eastern or Asian passengers,” she said.

“They are often forced to stay in the hold, where they are at greater risk of drowning if the boat capsizes and can become ill from breathing in the petrol fumes.

“Partly this is because African migrants - from countries like Eritrea and Somalia often - are not able to pay as much as others, and partly we think simply because of racism on the part of the people smugglers.”

In July last year, around 100 migrants were massacred by traffickers after they tried to escape a locked hold as fumes spread from the boat’s engine.

As the poisonous gas spread below deck, panic started and the passengers managed to force open the door, only to be met by traffickers armed with knives who started massacring them and throwing them into the sea.

Five men stabbed and assaulted passengers at random and threw them overboard, telling others not to react or they would suffer the same fate, police said.

Approximately 60 of the migrants were attacked and their bodies dumped, while around 50 are thought to have been thrown directly into the sea to drown.

Eighteen migrants were found dead in a tangled mass of bodies in the hull after succumbing to the fumes.

Survivors who were taken off the ship by Italian and Maltese authorities were described as dominantly Syrian and reports at the time said the dead migrants were “African”.

The five men arrested for their murders were from Saudi Arabia, Syria, the Occupied Palestinian Territories and Morocco.

Many of the estimated 900 migrants who drowned after a ship sailing from Libya capsized on Sunday had also been locked below the deck, according to a survivor.

The 32-year-old Bangladeshi man said he only lived because he was on an upper level of the vessel.

“I and the others managed to survive because we were outside, but many of the others remained prisoners in the hold of the boat because the traffickers had locked them in and they finished at the bottom of the sea,” he said.

Authorities, who have charged the Tunisian captain with reckless mass homicide, have not said how those migrants were divided up but they believe that the rush to escape after the boat collided with a container ship contributed to it capsizing.

The disaster came amid calls for action over rising numbers of deaths during voyages to Italy that have killed an estimated 1,700 people in the last week alone.

The crisis has sparked an emergency summit by European Union leaders to crack down on human trafficking and aid Italy’s rescue missions.