Thailand's success in attracting huge numbers of tourists has put some infrastructure for handling the influx under pressure, an economist with the World Bank says. "Bottlenecks are building up in destinations like Chiang Mai, Bangkok and Phuket, while infrastructure still hasn't expanded," Kiatipong Ariyapruchya said Monday. The economist also said that new destinations inside Thailand "must be introduced and monitored closely to support sustainable tourism." The industry has remained resilient despite a 2014 coup and a wave of deadly bombings in August this year that killed four Thai tourists and injured dozens, including foreigners. Last year, Thailand attracted a record 29.9 million visitors. The tourism ministry expects 32.4 million visitors this year while the tourism council says there could be 34.4 million in 2017. But tourism growth is putting airports and other aspects of infrastructure under strain. Infrastructure is a problem not just for tourism — a rare bright spot for the economy — but for growth in general. Airport plans In the World Economic Forum's Global Competitiveness Index 2016-17 , Thailand's infrastructure ranking was 49th, down from 38th in 2006-07. For airport congestion, help is planned. In June, Airports of Thailand, the country's main airport operator, said it intended to spend $5.5 billion over the next 15 years to expand six key airports. Thailand is in the middle of its tourist high season as travelers seeking respite from the cold in the Western Hemisphere flock to the country's beaches and islands. Sunsanee Fongcharoen, a Bangkok Airways passenger service supervisor at Suvarnabhumi Airport, one of the capital's two international airports, said bookings have increased twofold during the peak season, putting airport services under strain. There can be "passenger buildup at counter check-in areas and at immigration," Sunsanee said. In 2015, Suvarnabhumi Airport and Don Muang International Airport handled a total of 525,679 flights, up 15.6 percent from the previous year, according to the Thailand Board of Investmen