Hong Kong will likely be included in a UK plan to allow visitors without quarantine next month in a gradual reopening of borders, the head of London’s Heathrow airport, has told Bloomberg TV.

American tourists may be allowed to travel to Britain as well, Heathrow Chief Executive, John Holland-Kaye, said Thursday.

Hong Kong is likely to feature on the so-called U.K. 'Green List,' alongside Singapore, Australia, New Zealand, Israel and Iceland, plus some Caribbean destinations, he said.

Heathrow has been in constant communication with the government over the impact of the pandemic as well as plans for a resumption in travel.

Progress on vaccinations in the UK and US could allow the U.S. to be included on the 'Green List' of countries from which people will be able to travel to Britain without quarantine.

While it wouldn’t necessarily be reciprocal, the move would make it easier to travel to the U.K. from the U.S. than from some parts of the European Union, where coronavirus shots haven’t been rolled out as quickly.

Even a limited restart of U.S. services would come as a huge boost for Heathrow, which relies on the market for 20 percent of its traffic. The airport, Europe’s busiest before the pandemic, said passenger numbers remained stuck at just 9 percent of usual levels in the first quarter as current curbs limit operations at carriers such as British Airways and Virgin Atlantic Airways.

Holland-Kaye said he expects Prime Minister Boris Johnson’s government to publish the country list by the end of next week.

The government has targeted a reopening of travel by May 17, though the impact won’t be clear to airlines until criteria for how countries are divided between the three-category system are released.

Arrivals from places marked green will still require a minimum of two coronavirus tests, but those listed as amber or red will additionally face quarantines.

Some short-haul leisure destinations could be green-listed, but most likely only to island sunspots such as Spain’s Balearics and Canaries, Holland-Kaye said. Mainland Spain and Greece may not feature until June and July respectively.

The U.K. will confirm by early next month if international travel can resume on May 17, and which countries will fall into each category, a Department for Transport spokesman said in an email.

While a full deal with the U.S. might be difficult to reach in time for the mid-May target, a unilateral U.K. reopening could allow Americans to fly into the country for business and leisure trips, Holland-Kaye said.

In this scenario, Brits seeking to go to the U.S. would have to wait for the Biden administration to reciprocate.

Bloomberg reported last week on bilateral talks between the U.S. and U.K. transport secretaries on a potential travel corridor.

As with the U.S., restrictions in Australia and New Zealand would limit any significant bump-up in air travel until the measures were reciprocal. Both countries are currently closed to all except residents and citizens.

While the U.S. has restricted entry from European countries including the U.K., Americans are allowed leave and return freely. The policy has led to a mini-boom in pandemic travel to Cancun in Mexico.

UK may allow HK visitors without quarantine next month under border reopening plan