The arrival of coronavirus-infected passengers on flights from India remains a concern for other countries at a time when the Indian government is attempting to augment international air passenger traffic through bilateral travel bubbles.

This week, Saudi Arabia, a key destination for Indian migrant workers, suspended air travel from India amid concerns of potential imported cases.

This development comes after two airlines - Air India and Air India Express - were handed temporary bans last week by the authorities in Hong Kong and Dubai for flying in Covid-19 positive passengers to these two cities.

Hong Kong barred Air India for a fortnight until Oct 3, after one of its flights to the city last Friday carried six infected passengers.

This is the second time the authorities in Hong Kong have banned Air India. A similar two-week suspension order was handed out to the airline last month, after it flew 14 Covid-19 positive passengers to the city on Aug 11.

Prior to this, Air India Express was issued a 15-day ban by the Dubai Civil Aviation Authority on Sept 17. This was because the airline's ground-handling agents failed to prevent two passengers with positive Covid-19 reports from boarding flights to Dubai - one from Delhi on Aug 28 and the other from Jaipur on Sept 4.

The suspension order was, however, revoked last Friday following an apology and assurance of better pre-boarding checks, an Air India Express spokesman told The Straits Times.

India has recorded over 5.7 million confirmed Covid-19 cases, but serological surveys, which detect antibodies to determine exposure to the virus, show a far greater spread of the infection that is yet to show any convincing sign of having peaked.

As a result, several countries now require visitors flying in from India to produce a polymerase chain reaction test carried out within 72 hours before departure certifying them to be negative.

Hong Kong also requires visitors from India to have a negative "nucleic acid test" report conducted 72 hours prior to departure, along with proof that the test was conducted in a laboratory recognised by the local government. Travellers also must have a hotel room reservation in Hong Kong for not less than 14 days starting on the day of arrival.

An Air India spokesman told The Straits Times that the airline has been "strictly adhering" to all passenger screening requirements for flights to international destinations and that, wherever required, only passengers with Covid-19-negative reports are allowed on board.

He said passengers are tested again for Covid-19 after landing in Hong Kong and the results "may vary from the reports of tests conducted 72 hours before taking the flight". Hence, Air India cannot be held responsible for any discrepancies in passengers' test reports, he added.

The Indian government has a travel bubble arrangement with 13 countries to allow smoother international air passenger traffic.

Regular scheduled commercial flights have been suspended in India since March 25.