Rescuers restarted the search operation for 12 missing people on Saturday early morning with the Italian-flagged ferry still burning on the Ionian Sea off Corfu.
Overnight, patrol ships combed the area off the holiday island hoping to locate survivors, the Greek coastguard told the Agence France-Presse (AFP).
The fire and the heat on the ferry prevented rescuers from boarding on Saturday morning, but a helicopter, a frigate, a fire-fighting vessel and six tug boats were operating in the area more than 50 kilometers (30 miles) from Corfu.
Rescuers brought 280 passengers to Corfu after the blaze on the Euroferry Olympia broke out en route from Greece to Italy.
Officials say the cause of the fire remains unknown.
The coastguard said all of the missing are truck drivers – seven from Bulgaria, three from Greece, one from Turkey and one from Lithuania.
Truckers who were rescued from the vessel told Greece's public broadcaster on Saturday that some drivers preferred to sleep in their vehicles because the ship's cabins were overcrowded.
According to the Kathimerini newspaper, since June 2017 the Syndicate of Greek Professional Truck Drivers had warned about the conditions on Euroferry Olympia as well Euroferry Egnazia, both belonging to Grimaldi.
In a letter to the Greek marine ministry, they reported the air conditioning did not work in the cabins and there were not enough cabins for the number of passengers.
They had also complained about poor ventilation in the garage.
The 27-year-old ship's latest safety check was at Igoumenitsa on Feb. 16, the company said.
Black smoke was still billowing into the air Saturday morning, according to the Ert state-run television station, while some explosions were heard.
Grimaldi Lines, the owner of the vessel, claimed the fire "is currently under control," but the Greek Coast Guard Saturday morning couldn't confirm.
According to the company, the ferry was officially carrying 239 passengers and 51 crew, as well as 153 trucks and trailers and 32 passenger vehicles.
But raising concern about how many unofficial passengers were missing, the coastguard said two of the people rescued were not even on the list. Both were Afghans, the coastguard told the AFP.
The Bulgarian foreign ministry said 127 of its nationals were on the passenger list, including 37 truck drivers.
Another 24 were from Turkey, the country's NTV station said, while broadcaster ERT said 21 Greeks were onboard.
Among the rescued, nine people were taken to the hospital with breathing problems.
"Two Bulgarians were hospitalized; one had very low saturation and was intubated," Deputy Foreign Minister Velislava Petrova told a briefing Saturday.
'Jumping in the sea'
A specialized Greek rescue team that boarded the burning vessel halted work Friday evening because of the intense heat, dense smoke and power outage on the ship, Athens News Agency said.
One of the rescuers who went aboard the ferry on Friday was taken to the hospital with respiratory problems, the fire brigade told AFP.
"We waited for four hours before the rescue team came. We were trapped in the fire in the night; we only felt fire underneath our feet," Fahri Ozgen, one of the rescued passengers, told AFP. "Around 250 people were screaming, shouting, some of them were jumping into the sea. Some of our friends are still missing, we don't know where they are."
Some of the passengers lost everything in the fire. "We lost our money, passports, all our administrative documents, I don't even have shoes to cover my feet. We can't make any phone call," trucker Ali Duran said.
There is heavy maritime traffic between the western Greek ports of Igoumenitsa and Patras and Italy's Brindisi and Ancona.
The last shipboard fire in the Adriatic was in December 2014 on the Italian ferry Norman Atlantic. Thirteen people died in that blaze.