"We will see a considerable drop in tourism income," Andreas Andreadis, the head of Greece's tourism enterprises association SETE.L told Reuters. "A negative number, something like 10-15 percent."

In 2011, revenues rose by 10 percent to 10.5 billion euros. About 1.5 million more tourists visited the country last year, largely due to lower fares and political uprisings in rival holiday destinations Egypt and Tunisia, bringing the total number of visitors to a record high of 16.5 million.

Accounting for about 15 percent of output and one in five jobs, tourism is vital for Greece's economy. The latest estimates have dashed hopes that the country's ancient monuments and sun-drenched islands will be able to pull it out of the debt crisis.

(Reporting by Yvonne Bell and Renee Maltezou; Editing by Andrew Osborn)

• A Permanent Economic Emergency