ATHENS—Greece's tourism industry is counting on a million more visitors this year, something that would provide a welcome boost to the country's recession-ravaged economy.

Early bookings from sun-starved British and German tourists—Greece's two biggest visitor groups—are up by double-digit percentages, and airlines say they are adding more than a million new seats to and from the country to cope with demand. Those extra visitors will bring in €1 billion ($1.3 billion) more in revenue than last year, say industry officials, something that could add a percentage point of growth, boost tax collections and add tens of thousands of new jobs by the summer.

With its picturesque islands and sunny Mediterranean climate, Greece has long been a top tourist destination. Last year, tourism, which accounts for about one-sixth of gross domestic product and nearly 20% of jobs, welcomed some 16 million visitors who spent a combined €10 billion.

"This year, we are aiming for 17 million tourist arrivals and €11 billion in revenue," said Andreas Andreadis, president of the Association of Greek Tourism Enterprises, or SETE. "If nothing goes wrong from now until summer, we are looking at a million more arrivals."

Things that could go wrong include another round of the violent riots that have rocked Athens and scared away would-be visitors in the past two years. So too could another spate of small-scale terror attacks like the ones that hit Athens this year.