At least 78 migrants drowned on Wednesday and many are missing after their overloaded boat capsized and sank off Greece in one of Europe’s deadliest accidents this year, Reuters reported.

Authorities said 104 people had been rescued by midday, but it was not known how many were on board when the vessel sank, whose passengers, according to coast police, refused offers of help between Tuesday and Wednesday.

“We fear that the death toll will increase,” said an official from the Ministry of Maritime Transport, who spoke on condition of anonymity, according to News.ro.

Immigrants would refuse help from the Greek coast guard, authorities claim

Greece is one of the main routes to the European Union for refugees and migrants from the Middle East, Asia and Africa. Most of them reach the Greek islands from neighboring Turkey, but more and more boats are making the longer and more dangerous journey from Turkey to Italy via Greece.

The public broadcaster ERT reported that the sunken boat left the Libyan city of Tobruk south of the Greek island of Crete and was heading for Italy.

It is the biggest disaster to hit Greece this year and one of the worst in Europe. In February, 96 people died when their wooden boat ran aground on rocks off the coast of Calabria during a storm.

Filippo Grandi, the UN High Commissioner for Refugees, called on governments to work together to create safe corridors for people fleeing poverty and war. “Only sadness and anger after yet another tragedy at sea in the Mediterranean,” he wrote on Twitter.

Greece is currently governed by an interim government, and elections are scheduled for June 25.

The Greek coast guard said the vessel was first spotted on Tuesday evening by the EU border agency Frontex in international waters, about 80 km southwest of the southern Greek coastal town of Pylos. Then a Greek Coast Guard vessel approached the boat, which was heading for Italy, and offered to help. A large number of migrants on the outer deck “refused assistance and expressed a desire to continue their journey,” the coast guard said. A few hours later, the boat capsized and sank, prompting a search and rescue operation.

Most of them are immigrants, young people in their 20s

According to ERT, most of those on board were young people in their 20s. A spokesman for the Ministry of Maritime Transport said most were from Egypt, Syria and Pakistan, although Greek authorities did not confirm the ship’s port of departure.

Those who survived were taken to the city of Kalamata, where the visit of the country’s president, Kateryna Sakellaropoulou, was expected.

Greece was at the forefront of Europe’s migration crisis in 2015, when nearly 1 million people arrived on its islands from Turkey before heading north to wealthier European nations. These numbers have fallen sharply since an agreement reached in 2016 between Brussels and Ankara to stem the flow of migrants. Greece’s conservative government, led by Kyriakos Mitsotakis, said tough policies that included more border patrols and migrant camps under increased surveillance had helped keep arrivals low.

Some 72,000 refugees and migrants have arrived in European countries on the Mediterranean front this year, according to UN figures, with most arriving in Italy and around 6,500 in Greece.

According to the UN, almost 1,000 people have died or gone missing in the Mediterranean this year.