Survivors of a capsized migrant boat off Libya have told the aid group Save the Children that an estimated 400 people are believed to have drowned.
The Italian coastguard had helped rescue 144 people on Monday and immediately launched an air and sea search operation in hopes of finding others.
"According to their stories, they all departed from Libya, more than 550 people on the same boat that capsized only 24 hours after they departed," Carlotta Bellini, a Save the Children spokeswoman in Rome, told Al Jazera.
The coastguard said it assumed that there were many dead given the size of the ship and that nine bodies had been found.
The deaths, if confirmed, would add to the skyrocketing numbers of migrants lost at sea: The International Organization for Migration estimates that up to 3,072 migrants are believed to have died in the Mediterranean in 2014, compared to an estimate of 700 in 2013.
William Spindler, a specialist on asylum and refugee issues at the UNHCR, said that due to conflict in places like Syria and the Horn of Africa, the number of people trying to find safety in Europe has increased "enormously" since last year.
Spindler said that to end the tragedies at sea, people smuggling needs to be combated, and the capacity to rescue people at sea increased.
"At the same time we need to open the possibility for refugees to come legally to Europe so that they don't need to take these dangerous journeys," he told Al Jazeera.
"And very importantly, we need to help countries that are hosting the vast majority of refugees in the world, countries such as Lebanon, Jordan, Sudan, Ethiopia, and Kenya ... We need to make sure they can continue to keep refugees safe - because otherwise refugees will continue these journeys and risk their lives to find safety in Europe."
The UN refugee agency, the UNHCR, said Italy's coastguard had saved about 8,500 migrants and refugees in the Mediterranean since Friday.
"Those rescued since last Friday included an estimated 3,000 people in four boats and 16 dinghies rescued on Monday," the agency said in a statement.
"What we are hearing from the coast guard is that about 2,000 rescued migrants who are still at sea on boats heading to the Italian shore," said Al Jazeera's Paul Brennan, reporting from the Italian port of Catania.
Earlier on Tuesday, the European Union's top migration official said the EU must quickly adapt to the growing numbers of migrants trying to reach its shores.
"The unprecedented influx of migrants at our borders, and in particular refugees, is unfortunately the new norm and we will need to adjust our responses accordingly," the EU's commissioner for migration, Dimitris Avramopoulos, told lawmakers in Brussels.
More than 280,000 people entered the European Union illegally last year. Many came from Syria, Eritrea and Somalia and made the perilous sea journey from conflict-torn Libya.
European coastguards have been overwhelmed by the numbers. Since the weather has begun to warm, even more people have been fleeing conflict and poverty, trying to reach Europe.
Source: Al Jazeera and agencies