Rescuers were scouring the seas off Greece on Saturday in a massive search operation as hopes dwindled for survivors of a shipwreck that estimated killed 298 Pakistan nationals. 

The ship was carrying 310 Pakistan nationals along with other migrants when it met the accident earlier this week. The Pakistan embassy in Greece has confirmed that 12 of the citizens had been rescued, adding that the local authorities had managed to recover 78 bodies as search operation continues for fourth day. 

The embassy said the identity of the bodies was yet to be confirmed. It asked the families in Pakistan, whose beloved ones were on the boat, to send verified reports of their DNA tests for crossmatch.  

Sources said over 130 Pakistani's belonged to the Kashmir region. 

Earlier on Wednesday, hundreds of people were thought to have packed a fishing boat that capsized in international waters about 50 miles (80 km) from the southern coastal town of Pylos, while being shadowed by the Greek coast guard.

As dawn broke on Thursday, a coast guard vessel sailed into the nearby port city of Kalamata, transferring victims of the year's deadliest shipwreck off Greece. By the early hours, the survivors there numbered 104 out of several hundreds.

Authorities said it was unclear how many had been aboard the vessel, and they were investigating one account from a European rescue-support charity that there could have been 750 people on the 20- to 30 metre-long (65- to 100- foot-long) boat. The U.N.'s International Organization for Migration said initial reports suggested up to 400 people were aboard.

Government officials said the vessel had set off from the Libyan port of Tobruk, but added that migrants on the boat had persistently refused offers of help from Greek authorities.

"It was a fishing boat packed with people who refused our assistance because they wanted to go to Italy," coast guard spokesperson Nikos Alexiou told broadcaster Skai TV.

"We stayed beside it in case it needed our assistance which they had refused."

Aerial pictures released by the Greek coast guard showed dozens of people on the boat's upper and lower decks looking up, some with arms outstretched, hours before it sank.

Greece is one of the main routes into the European Union for refugees and migrants from the Middle East, Asia and Africa.

Under a conservative government, in power until last month, authorities have taken a harder stance on migration, building walled camps and boosting border controls.

Libya, which has had little stability or security since a NATO-backed uprising in 2011, is a major launching point for those seeking to reach Europe by sea.

People-smuggling networks are mainly run by military factions that control coastal areas.

The United Nations has registered more than 20,000 deaths and disappearances in the central Mediterranean since 2014, making it the most dangerous migrant crossing in the world.