Prime Minister Prayut Chan-o-cha yesterday ordered the Royal Thai Air Force (RTAF) to help expedite immigration and customs processes to help reduce waiting times at airports.

It is the latest effort to streamline the process of entering the kingdom and reduce long queues for passengers arriving on international flights.

The Immigration Bureau is also seeking to amend the immigration law to exempt Thai nationals from filling out immigration documents known as TM.6 cards. It is not known at this stage when this will materialise.

The bureau's actions were prompted by huge queues at Don Mueang airport last weekend, when thousands of visitors had to wait several hours to clear immigration and customs.

Not long after, international arrivals at Suvarnabhumi airport experienced similar queues on Wednesday afternoon after 20 aircraft landed between 3pm-4pm, discharging 4,600 passengers.

However, the Immigration Division 2 said immigration officers were at full strength at the time and were able to clear passengers within 57 minutes.

In response to the incidents, Gen Prayut said yesterday he had told the Immigration Bureau to open all counters for service, and in case of a shortage of staff, RTAF officers would be brought in to help. The prime minister said there are several factors contributing to long immigration waits, including limited space at Don Mueang airport.

While the airport can handle 1,000-2,800 people an hour, there are as many as 4,000 passengers arriving at the same time due to delayed flights, said Gen Prayut, adding that authorities would look into whether the airport can be expanded.

"We have to investigate when congestion occurs and why. I've told the Immigration Bureau to open all immigration counters. And I've asked the air force commander to bring in personnel to help when they are short staffed.

"The Transport Ministry, the Airports of Thailand and the Immigration Bureau have been assigned to deal with the task. If this isn't enough to handle the issue, we have to figure something else out," Gen Prayut said.

Immigration Bureau commissioner Nathathorn Prousoontorn said talks would be held among the authorities concerned including the Airports of Thailand on the prime minister's directive.

However, the commissioner insisted that RTAF personnel would not be allowed to process passengers through immigration because that jurisdiction belongs to immigration officials only under the immigration law. He added that their assistance could be used in other areas.

He said discussions should be concluded in a week, and assistance from the RTAF might not be needed if things work out.

Pol Lt Gen Nathathorn said that as a relief measure 200 immigration officers at other border checkpoints have been called in to help at three airports -- Don Mueang, Suvarnabhumi and Phuket -- that are seeing an unusual increase in passengers despite it being the low season.

Immigration counters at the Don Mueang will be increased from 21 to 39 in a few weeks, he said.

He admitted that immigration officer numbers at the international airports are low, and that is beyond the bureau's control, saying the Royal Thai Police (RTP) is responsible for job allocating.

Don Mueang and Suvarnabhumi airports have seen a steady increase in air travel over the past few years.

According to the Immigration Bureau, in July 2014, a few months after the coup, 526,224 passengers passed through Don Mueang airport.

During the high season in December last year, that number stood at 605,435 passengers and in July this year, passengers passing through Don Mueang stood at 1.22 million.

The number of passengers passing through Suvarnabhumi in July 2014 stood at 1.84 million. That figure rose to 2.9 million in December last year and shot up to 3.04 million in July this year.

Meanwhile, RTAF spokesman VAM Pongsak Semachai said the RTAF would have to study the law to determine what it could do to help.

He said air force commander Johm Rungswang has asked for a review of the law and the air force's rule book to see how the air force can help in this matter.

"We need to see if it is possible for air force officers to conduct immigration duties," he said.

National police chief Chakthip Chaijinda yesterday said that forward command centres at five airports -- Suvarnabhumi, Don Mueang, Phuket, Chiang Mai and Hat Yai -- were told to speed up immigration procedures. Action would be taken against them if they do not.