A passenger was on Sunday found alive aboard a ferry that has been ablaze off Greece for three days, coastguards said, but 11 truck drivers are still missing.

Rescuers spotted the 21-year-old man on the stern of the stricken vessel as it was being towed to port. 

The ferry was 1.5 miles (about two kilometres) off the northern part of Corfu, the Coastguard said.

"Tell me I'm alive," the truck driver, who said he was from Belarus, told rescuers, according to the Proto Thema news website.

Clad in tan shorts and a black t-shirt, he climbed down a ladder into a rescue boat, according to images from the iefimerida news website.

"I was in my cabin. I went to the lower deck. I heard voices. I did not see others," the survivor told rescuers.

The news of the man's survival raised hopes further lives might be saved. 

"There is optimism. Given the fact this man managed to get to the upper deck in these conditions," coastguard spokesman Nikos Alexiou told Ert television. 

He added that first aid was given to the driver who was to be transferred by ambulance boat to the port of Corfu. 

According to the fire brigade, 40 firemen were deployed in the area on Sunday morning to help with rescue efforts.  

The blaze broke out on the Italian-flagged Euroferry Olympia late  Thursday as it sailed from Igoumenitsa in Greece to Brindisi in Italy, with nearly 300 people aboard.

- 'Corrosive goods' -
Criticism has mounted over conditions aboard the vessel, which was reported to be carrying fuel and "corrosive, dangerous goods".

Rescuers managed to save 281 passengers on Friday, evacuating them to Corfu, but 12 lorry drivers remained missing.

The man rescued on Sunday was one of those drivers, the coastguard said.

Authorities initially gave the missing as seven from Bulgaria, three from Greece, one from Turkey and one from Lithuania.

On Sunday, they said there was an error and the missing Lithuanian was actually the man saved, who was from Belarus. 

The drivers are believed to have been asleep inside their lorries when the blaze broke out.

Olympia was carrying an estimated 800 cubic metres of fuel and 23 tons of "corrosive dangerous goods", according to Italy's environment ministry which said on Saturday that a "possible spill" was detected after a fly-over by an Italian coastguard aircraft.

-- 'Miserable' conditions --
The vessel was officially carrying 239 passengers and 51 crew, as well as 153 trucks and trailers and 32 passenger vehicles, the Grimaldi company has said.  

But the coastguard has said two of the 280 people rescued were Afghans not on the manifest, sparking fears that more undocumented passengers could also be missing. 

The missing truckers reportedly slept in their vehicles because cabins on the vessel were overcrowded.

Ilias Gerontidakis, the son of a missing Greek trucker, told the Proto Thema online newspaper the Olympia was "miserable from every point of view".  

"It had bed bugs, it was dirty, it had no security systems," he said as he waited at the port for news.

"It had 150 lorries inside. Normally it should have 70 to 75 cabins, but it only has 50. They force us to sleep four people in a cabin", he said. 

"My father, from what I was told, slept in the truck."

The news of the rescue of the Belarussian rippled through relatives of those still missing who are waiting for news of loved ones in the port of Corfu.

Ert showed emotional scenes of a woman being carried away after fainting. 

The last shipboard fire in the Adriatic occurred in December 2014 on the Italian ferry Norman Atlantic. Thirteen people died in that blaze.