Rescuers picked up the search for 12 missing people at the break of dawn Saturday after an Italian-flagged ferry caught fire on the Ionian Sea the previous day.
Overnight, patrol ships combed the area off Corfu island hoping to locate survivors, the Greek coastguard told AFP.
Rescuers brought 278 passengers to Corfu after the blaze on the Euroferry Olympia broke out en route from Greece to Italy.
Officials have said the cause of the fire remains unknown.
According to the coastguard, all of the still-missing people are truck drivers, nine from Bulgaria and three from Greece.
Truckers who were rescued from the vessel told Greece's public broadcaster on Saturday that some drivers prefered to sleep in their vehicles because the ship cabins were overcrowded.
Grimaldi Lines, the owner of the vessel, said late last night the fire "is currently under control" but Greek Coast-Guard Saturday morning didn'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 for how many potential unofficial passengers could still be missing, the coastgaurd said two of the rescued people were not included on the manifest.
Both were Afghans, the coastguard told 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 there were 21 Greeks onboard.
Among the rescued, 10 were taken to hospital with breathing difficulties and minor injuries, ERT said.
A specialised Greek rescue team that boarded the burning vessel ceased its efforts Friday evening because of the high heat on the ship, the dense smoke and the darkness, according to Athens News Agency.
The 27-year-old ship's latest safety check was at Igoumenitsa on February 16, the company said.
There is heavy maritime traffic between the western Greek ports of Igoumenitsa and Patras and the Italian ports of Brindisi and Ancona.
The last shipboard fire in the Adriatic occurred in December 2014 on the Italian ferry Norman Atlantic. Thirteen people died in that blaze.