WATCH: The latest on the search for survivors near Greece

The search for survivors off Greece's Peloponnese peninsula following a shipwreck that has killed at least 78 migrants has been extended until Sunday.

The coastguard has so far rescued 104 people from the fishing boat, but hopes of finding anyone alive are fading "by the minute," according to officials.  

Reports have suggested between 400 and 750 people had packed the vessel that capsized and sank early on Wednesday morning in deep waters about 80 kilometers from the southern coastal town of Pylos.

Greek authorities said the 104 survivors and 78 bodies of the dead were brought ashore in the immediate aftermath. 

Most of the people on board were from Egypt, Syria and Pakistan, Greek government officials have said. Many were children and may have drowned inside the crowded vessel's hold.

While the exact number of passengers on the rusty trawler is unknown, hundreds remain missing, and relatives and activists have said at least 141 Syrians were aboard.

Iyad from Jassem in the southern province of Daraa, the cradle of Syria's 12-year civil war, said his 19-year-old son Ali was still unaccounted for.

"I have had no news of my son. I haven't spoken to him. I haven't heard his voice," said Iyad, who works at a school. "His mother hasn't stopped crying for three days."

The 47-year-old said he had heard of two Greek reports - one listing his son among the survivors and another among the dead.

"I still have hope that he will be among the survivors," Iyad added. "We are praying to God day and night. "He told us he wanted to go work in a restaurant, but we didn't know he wanted to take a boat. If we'd known, we wouldn't have allowed him to go."

Twelve Pakistanis were among the survivors from the boat, the Ministry of Foreign Affairs said on Saturday. 

More problems were building at sea over the weekend. Italy alerted Greece to a vessel holding dozens of migrants sailing off the southern coastal town of Pylos, two sources said.

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