At least 78 people drowned in the Aegean Sea after a large fishing boat carrying migrants sank early Wednesday, the Greek Shipping Ministry said, in the deadliest such episode off the country’s coast since the height of the 2015 migration crisis.
More than 100 people were rescued, but the Greek Coast Guard warned that the death toll would probably increase.
The boat foundered about 50 miles southwest of the city of Pylos, in southern Greece, after the authorities were alerted to its unusual movements on Tuesday, according to a statement from the Greek Coast Guard.
The coast guard said that the boat had declined assistance offered by the authorities, but that cargo ships in the area had given the rescued migrants food and water after the boat sank.
A Greek Shipping Ministry official said that the boat had departed from Tobruk, Libya, and had been traveling to Italy.
The cause of the sinking was unclear as of Wednesday afternoon.
The Greek authorities said that the coast guard and the military had deployed a large number of vessels in a “wide-ranging search and rescue operation” to reach survivors and locate the dead, many of whom were said to be migrants from Egypt, Pakistan and Syria.
It was unclear how many people were still missing, but interviews with survivors were expected to shed more light on the scale of the tragedy.
President Katerina Sakellaropoulou was on her way to the port of Kalamata, in southwestern Greece, her office said. The local authorities there have established an open-air clinic to provide first aid to survivors.
It was the deadliest such episode off the Greek coast since 70 people died when a boat carrying migrants sank near the island off Lesbos in October 2015, according to the International Organization for Migration.
Last year, nearly 3,800 migrants died on routes within and from the Middle East and North Africa region, according to a new annual report by the organization — the highest death toll in five years, the report said. And given the scarcity of official data, the actual number of deaths on those migratory routes is probably much higher, it said.
“As many as 84 percent of those who perished along sea routes remain unidentified, leaving desperate families in search of answers,” the report said.
The sinking on Wednesday occurred during an election campaign in Greece in which the country’s policy on migrants has been a central issue. The current prime minister, Kyriakos Mitsotakis, has defended his government’s tougher migration policy, arguing that the previous administration’s more lenient stance had resulted in undue pressure on the country and a rise in deaths at sea.
Mr. Mitsotakis imposed a crackdown on migration during his time in power, heightening border controls in an effort that led to a 90 percent drop in migrant arrivals since 2015. Rights groups have accused his government of illegally pushing back migrants at sea and building camps with prisonlike conditions, although many people in Greece, particularly in border areas, have welcomed the reduced influx.
Greece’s Migration Ministry said that the fatal sinking also pointed to an urgent need to address the smuggling of migrants across international borders.
“The sinking once again brings to the fore, in the most tragic way possible, the need to break international smuggling rackets which put the lives of migrants in danger,” the ministry said in a statement.
