ROME, Italy (CNN) -- Up to 75 migrants are missing and feared dead after a harrowing 20-day journey from northern Africa to Europe, a United Nations agency said Friday.
Authorities in Italy rescued five Eritrean nationals Thursday in the waters off an Italian island. Survivors said that up to 75 other migrants, mostly fellow Eritreans, died as they tried to reach Europe, said Andrej Mahecic, a spokesman for the U.N. High Commissioner for Refugees.
"We are shocked by the accounts ... from five Eritreans who are allegedly the only survivors from a boat that set out from Libya 20 days ago," Mahecic said Friday. "The survivors are in very poor health and were taken to Italy for treatment."
Italian authorities Friday were patrolling the waters off Lampedusa, an island in the Mediterranean Sea roughly half way between Sicily and North Africa.
About 80 migrants were aboard the boat when it ran out of fuel and got lost about two days into the journey, said Laura Boldrini, also with the U.N. High Commissioner for Refugees.
She said she based her information on accounts that a survivor provided to one of her colleagues on Lampedusa.
After some people on the boat got sick and died, the others dumped their bodies into the sea for fear of also getting sick, Boldrini said.
Several migrants screamed for help in English when their boat passed other vessels, but only one fishing boat stopped to give the migrants some food and water, Boldrini said, citing the account that a survivor provided to her colleague.
Those reports alarmed the U.N. refugee agency.
"This is contrary to the long-standing maritime tradition of rescue at sea" Mahecic said.
Italian police in Rome confirmed that naval officers rescued five Eritreans off the coast of Lampedusa, but they declined to provide additional details.
The number of illegal immigrants traveling to Italy and other European destinations has increased in recent years, with many Africans fleeing faltering economies and repressive regimes for the chance of a better future.
Lampedusa has seen arrivals of illegal immigrants double in recent years, from 14,855 in 2005 to 30,657 last year, according to the Italian Interior Ministry.
In the first eight months of this year, though, the number of illegal immigrants arriving at Lampedusa declined compared with the past few years, with 7,567 arrivals recorded through August 19, according to Interior Ministry figures.