WASHINGTON: The United States is preparing for long lines and delays on Monday when restrictions are lifted on non-U.S. citizen international travellers who are fully vaccinated against the coronavirus, a senior official told Reuters on Friday.

President Joe Biden's administration "expects pent-up demand for travel, which means longer than normal wait times for travelers," the official said. The government was boosting staffing to pre-pandemic levels but "long lines are expected in the initial days."

The United States on Monday is lifting travel restrictions for fully vaccinated air travelers from 33 countries and at its land borders with Mexico and Canada, ending the historic entry bans to address the spread of COVID-19 for much of the world's population.

The official said land border traffic has been about 70% of 2019 levels on the Southwest border and 30% of 2019 levels on the Northern border.

U.S. Customs and Border Protection "will continue to adjust its resources to meet traffic workload demands and ensure operational security, while balancing its trade facilitation and national security mission," the official said. Travelers should familiarize themselves with the new guidelines and have their documentation ready in advance, the official said.

Delta Air Lines Chief Executive Ed Bastian has also said travelers should be prepared for long lines initially from Monday.

"It's going to be a bit sloppy at first. I can assure you, there will be lines unfortunately ... but we'll get it sorted out," Bastian said.

Delta said in the six weeks since the U.S reopening was announced it has had a 450% increase in international point-of-sale bookings.

United Airlines is expecting about 50% more total international inbound passengers Monday compared to Nov. 1 when it had about 20,000.

The Biden administration has held multiple calls with U.S. airlines to prepare for the influx of additional travelers who will begin arriving at the country's airports.

The restrictions, put in place in early 2020 during the pandemic, barred most non-U.S. citizens who within the last 14 days had been in any of 33 countries - the 26 Schengen nations in Europe without border controls, China, India, South Africa, Iran, Brazil, Britain and Ireland.

Also on Monday, new contact tracing rules will take effect requiring airlines to collect information from international air passengers if needed "to follow up with travelers who have been exposed to COVID-19 variants or other pathogens."