According to the NTTO, the issues mean that an estimated 4.5 million records received from US Customs and Border Protection relating to US arrivals were incorrectly logged.

The NTTO believes a “meaningful and increasing number” of non-US citizens travelling on visas to the US were incorrectly categorised as US residents, meaning that visitor arrivals figures for 2017 were lower than they should be.

Visitors arriving into airports and filling out their details at automated kiosks were logged as US residents if they left the “Country of Residence” field blank.

Speaking at IPW in Denver on Tuesday, Roger Dow, president of the US Travel Association, commented on the issue.

“According to NTTO data, international travel was down by between four and six percent in 2017, but this wasn’t making sense when we were speaking to our US partners, who were often saying their visitor numbers were flat for the year, or even up.”

“The difficulty was that inbound foreign citizens were being counted as returning US citizens,” he explained.

Dow reassured IPW delegates that the Department of Commerce is addressing the problem to “fix it fast”, and that correcting the data was a “high priority for the Department of Homeland Security.”

He predicted the problem would be rectified within the next six months.