Tourism grew between 3.5 percent and 4 percent in 2012, the secretary general of the UNWTO said, with the billionth tourist expected to touch down somewhere in the world on Thursday.

Chinese tourists, whose numbers increased 30 percent year-on-year, and their Russian counterparts, whose numbers swelled 16 percent, offer big opportunities for traditional tourist destinations like the Mediterranean, but countries must do more to make travelling easier for them, the UN said.

"It is not acceptable any more to spend so much money on promoting some destinations and then spend even more money to tell people not to come," the UN's Taleb Rifai said in an interview with Reuters.

Rifai said Mediterranean countries must relax visa restrictions for visitors from nations like Brazil, Russia, India and China, where growth has outpaced recession-hit Europe and emerging middle classes are increasingly travelling outside national borders.

"We need to be specially tailoring and designing policies. A Chinese is not going to come to the Mediterranean just to visit one destination...These are the travellers of the future."

He also warned against tax hikes that could scare away tourists.

Many European countries have raised taxes as part of austerity programmes to get government finances back on track. When Spain raised valued added tax VAT.L for the leisure sector to 10 percent from 8 percent this year, the industry estimated it could lose around 2 billion euros in revenue.

"We need to be sure that these taxes are designed in policy and in practice so that they do not choke the industry and in layman's terms, kill the goose that lays the egg," he said.

Spain, where tourism accounts for 11 percent of economic output, and its highly indebted euro zone peer Greece, did not fare as well from unrest in the Middle East this year as last.

Visitors shunned North Africa last year as Arab Spring protests spread across the region, redirecting up to 7.5 million tourists to sunny Mediterranean destinations like Spain, Greece and the Balkans.

Tourism to Spain grew 3 percent this year, compared to 8 percent in 2011 when unrest in Arab countries was flaring up.

The UNWTO, which is based in Madrid, expects the number of world travellers to reach 1.8 billion by 2020, when one in 10 people will be employed in the travel and tourism industry. (Reporting by Clare Kane, editing by Paul Casciato)

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