The Immigration Bureau on Wednesday increased its capacity to handle passenger arrivals at Suvarnabhumi airport after complaints about lengthy delays on Sunday.
A bureau spokesman said arrivals' queues peaked on Sundays between 1pm and 5pm, with 3,000-4,000 passengers landing per hour at Suvarnabhumi airport.
On that day immigration increased staffing and average waiting time was about an hour, he said.
Immigration officers took about 45 seconds to check each arrival, using a blacklist and collecting biometrics.
"Immigration police must watch out for foreigners who may arrive in the guise of a tourist for criminal purposes, or maybe to cause a disturbance during the coming Asia-Pacific Economic Cooperation summit," he said.
To cope with the increasing traffic, Airports of Thailand had increased the number of immigration booths from 92 to 119 and more immigration officers were on duty from Wednesday on. This would allow them to handle about 6,500 arrivals per hour without compromising security, he said.
Earlier the capacity was about 5,500 travellers an hour.
He said 45,000-50,000 foreigners were now arriving in the country daily by air and land.
