Thailand's tourism industry will face greater risks next year if the government continues to restrict foreign travellers from entering the country, says the Bank of Thailand.

Foreign arrivals could be downgraded from a projection of 8 million this year and 16 million next year, said Don Nakornthab, senior director of the economic and policy department.

The Tourism and Sports Ministry and the National Economic and Social Development Council already cut their projections for this year's foreign tourist arrivals to 6.7 million and next year's to 12 million.

The difference of 1.3 million foreign arrivals this year in projections from the central bank and the two state organisations would result in a 0.5% decline in Thailand's GDP, said Mr Don.

Thailand received no foreign tourist arrivals for the fourth consecutive month in July as international travel restrictions remain in place to safeguard against a second outbreak.

Foreign arrivals to Thailand reached 40 million in 2019, with revenue generated from the tourism industry contributing almost 20% of GDP.

With inbound flight restrictions still in place, the ratio of foreign travellers is expected to shrink by 100% year-on-year between April and December, said Mr Don.

He said the government should consider looking into proper measures to allow foreign travellers to return to stir tourism and economic growth momentum.

"If foreign travellers still cannot visit the country, this will impact Thailand's economic growth more severely next year. The government should strike a balance between tourism measures and outbreak containment," said Mr Don.

The central bank also factored in the possibility of a second wave outbreak, as in other Asian countries. New infections of around 20-30 cases per day are acceptable, he said.