According to survivors of a shipwreck off Lampedusa, 41 migrants have died.

Rescuers discovered four people who survived the tragedy on a boat that sank on its way from Tunisia to Italy.

Originally from Guinea and the Ivory Coast, the four survivors reached Lampedusa on Wednesday.

So far this year, more than 1,800 people have died crossing from North Africa to Europe.

Salvatore Vella, the local public prosecutor, said an investigation had been launched.

A 13-year-old boy, two men, and a woman told rescuers they were on a boat carrying 45 people, including three children.

After being hit by a big wave, the boat, which was about 7m (20ft) long, sank within hours after leaving Sfax on Thursday last week. Life jackets were worn by only 15 people, but they did not appear to be effective in saving their lives.

After the shipwreck, the four survivors floated on inner tubes and lifejackets until they found another empty boat at sea, where they drifted for several days before being rescued by the Italian Red Cross.

Adrian Chiaramonte, the doctor who treated the four survivors, said they had only minor injuries when they arrived in Lampedusa.

“The tragedy was what really struck us,” he said.

Apparently, a first ship ignored them when they encountered it.

An hour later, a helicopter spotted them, and an hour after that, an oil tanker picked them up.”

On Sunday, the Italian coast guard reported two shipwrecks in the area, but it is unclear whether this vessel is among them.

According to the International Organization for Migration (IOM), migrants would have had little chance of surviving.

According to IOM spokesman Flavio Di Giacomo, sub-Saharan migrants [leaving Tunisia] are forced to use these low-cost iron boats which breakdown after 20 to 30 hours of navigation. “These boats capsize easily in this kind of sea,” he added.

According to Tunisian authorities, Sfax is a popular gateway for migrants seeking a better life in Europe, about 80 miles (130km) from Lampedusa.

Over the past few days, Italian patrol boats and charity groups have rescued another 2,000 people on Lampedusa.

Recent months have seen an increase in racist attacks on black Africans in Tunisia.

Since 2014, the central Mediterranean has been the most dangerous migrant crossing in the world, according to the United Nations.

To curb “irregular” migration, the EU signed a $118 million deal with Tunisia last month.

It will be used to stop smuggling, strengthen borders, and return migrants.

As a result of Italy’s far-right government’s policy, rescue ships are forced to dock at ports further away instead of disembarking rescued migrants in Lampedusa or Sicily.

However, NGOs complain that the policy reduces the amount of time they can spend patrolling areas where shipwrecks are more common.