The United Nations refugee agency says at least 300 migrants are missing and likely dead after they tried to cross the Mediterranean Sea in inflatable boats.
The U.N. High Commissioner for Refugees said Wednesday that it is "shocked" by new information that shows the scale of the tragedy is much larger than initially reported.
On Tuesday, Italian authorities said at least 29 African migrants died of hypothermia trying to cross the sea from Libya in frigid weather.
Since then, reports have emerged that four inflatable boats had left Libya together carrying a total of more than 400 people.
The UNHCR says the Italian coast guard brought 110 survivors to safety on the Italian island of Lampedusa.
The migrants had been at sea for days without food or fresh water.
A UNHCR spokeswoman, Carlotta Sami, told reporters the survivors will be transferred as quickly as possible to the mainland.
"The survivors are taken to the first reception center in Lampedusa that now is working at full scale," she said. "They receive assistance, they receive food, they receive medical assistance, they receive clothes. They arrived almost naked you know, they arrived without anything. And then within 24 hours, maximum 72 hours, they are transferred to other centers on the mainland."
Vincent Cochetel, UNHCR's Europe bureau director, warned Wednesday that a better search-and-rescue mission must be put into place to prevent future loss of life.
In an official statement, he said: "This is a tragedy on an enormous scale and a stark reminder that more lives could be lost if those seeking safety are left at the mercy of the sea."
The UNHCR has reiterated its concern about a new, European Union-funded search-and-rescue mission called Triton, which is run by the EU border protection agency. UNHCR said the mission "is not focused on search and rescue and is not providing the necessary tools to cope with the scale of the crisis." It said saving lives must be a priority for the European Union.
Triton replaced a more expansive search-and-rescue operation funded by the Italian government.
Lampedusa is about 110 kilometers from the African mainland, and is a major destination for illegal migrants trying to get to Europe.
A record 170,000 migrants crossed the Mediterranean Sea into Europe in 2014, one quarter of them fleeing the violence in Syria. More than 3,000 others died attempting the journey.
Experts say the volume of migration in 2015 already looks to be outpacing last year.