ATHENS- Eleven passengers were missing after a blaze engulfed a ferry sailing from Greece to Italy early on Friday while an operation was under way to try to rescue two people trapped in the ship's garage, the Greek coastguard said.

A total of 239 passengers and 51 crew were onboard the Italian-flagged Euroferry Olympia when the fire broke out, and rescue vessels had taken most of them to the island of Corfu where ambulances were waiting.

The fire was still burning by Friday afternoon and aerial footage released by the coastguard showed rows of burnt trucks on the blackened deck after flames swept through the 183-metre (600-foot) ferry that had been making a nine-hour journey through the night.

"The worst thing is the cars in the garage are glued next to each other, there is no escape route," one Greek truck driver, who did not give his name, said after arriving on Corfu.

A helicopter was on standby to airlift out two passengers trapped in the ship's garage, the coastguard said, as well as confirming 11 passengers were missing as fire crews tried to douse the flames.

The cause of the blaze was still being investigated, Greek authorities said.

At least 10 people had been taking to a Corfu hospital, most with breathing problems, a Greek health ministry official told state television, and there were no immediate reports of severe injuries.

Earlier on Friday, passengers huddled in yellow blankets on an Italian rescue vessel as huge plumes of smoke poured out of the ferry, one video showed. The words "May Day" were repeatedly blasting from the speakers, in the footage uploaded on Greek news website Proto Thema.

The ferry sailed from Igoumenitsa, the largest port in western Greece, and was headed to the Italian port of Brindisi. It carried 153 vehicles, many of them trucks, Grimaldi Lines, the owner of the vessel, said.

The fire broke out when the ship was near Corfu in the Ionian Sea. Hours after the alarm was raised, the vessel was still ablaze, drifting in Albanian waters, Grimaldi Lines said.

Grimaldi Lines spokesman Paul Kyprianou told Reuters that there were indications the fire started in one of its holds. The company was making every effort to help the passengers - most of them from Bulgaria, Romania and Turkey - get home, he added.

"The flames were incredibly high, we were a few miles away from the ferry when it happened," Colonello Felice Lodovico Simone Cicchetti from Italy's financial police, who took part in the rescue operation, said.

"The fire was so big and fast that in a matter of five minutes it became unmanageable for the people aboard."

In 2014, 10 people were killed when the car ferry Norman Atlantic carrying 466 passengers and crew caught fire while sailing from Greece to Italy.

(Additional reporting by Karolina Tagaris, Renee Maltezou and Lefteris Papadimas in Athens and Giulia Segreti in Rome; Writing by Karolina Tagaris; Editing by Alison Williams) ((karolina.tagaris@thomsonreuters.com; +30 210 3376 455;))