The UN refugee agency has said the death toll in the Mediterranean boat tragedy when hundreds of immigrants attempted to reach Europe stands at 800.

After interviewing most of the 27 people, who survived the perilous journey crossing from Libya, the UN said there were more than 800 people of various nationalities onboard the wrecked vessel.

"We can say that 800 are dead," Carlotta Sami, spokesperson for the United Nations High Commissioner for Refugees in Italy told reporters.

"There were a little over 800 people on board, including children aged between 10 and 12. There were Syrians about 150 Eritreans, Somalis... They had left Tripoli at about 08:00 am on Saturday [18 April]," said Sami.

The victims included nationals from Bangladesh, Gambia, Mali, and Senegal. The survivors were taken in a coast guard vessel to the Italian port of Catania, while one of them was admitted at a hospital.

The desperate immigrants were seeking a better life in Europe when their ship capsized between Italy and Libya in the Mediterranean sea. The disaster took place at about 200kms from the island of Lampedusa and 32kms from Libya. The African nation provides a perfect haven for human traffickers.

Two of the survivors – the captain and his deputy – have been arrested for suspected human trafficking by the Italian police. The captain is believed to be a Tunisian national while his deputy is said to be from Syria.

Subsequent to the intense pressure on handling the mounting migrant crisis, the EU has agreed to step up search and rescue efforts in the Mediterranean.

Urging the EU states to do more in addressing the crisis, the UN Human Rights chief Zeid Ra'ad al Hussein said: "Europe is turning its back on some of the most vulnerable migrants in the world, and risk turning the Mediterranean into a vast cemetery. These deaths, and the hundreds of others that preceded them in recent months were sadly predictable."