Dozens of passengers aboard a plane traveling from the Indian capital New Delhi to Hong Kong have tested positive for the coronavirus amid the worst COVID-19 spike in India and preceding a flight ban from the Asian finance and transport hub.

At least 53 passengers tested positive after taking a flight run by Indian operator Vistara on April 4. The positive tests are significant as Hong Kong is regularly recording fewer daily cases than the total detected on the flight since it brought a fourth wave under control in January.

Authorities have now imposed a two-week ban on all flights from India, Pakistan and the Philippines that began on Monday, categorizing the countries as "extremely high risk" after detecting the N501Y mutant coronavirus strain for the first time in the local community.

India is battling skyrocketing infections, with hospitals running out of beds and the government forced to reimpose economically painful restrictions. Its capital New Delhi went into lockdown starting Monday night as officials scramble to get the surging cases under control.

The Vistara aircraft can hold 188 passengers, but Hong Kong authorities did not announce how many it had been carrying.

The positive coronavirus results surfaced while the arrivals were undergoing Hong Kong's mandatory three-week quarantine period, one of the strictest entry regimes in the world.

All travellers flying into the territory from 25 places deemed high risk, including Britain, South Africa, India, Pakistan and the United States, must also provide a negative test taken within 72 hours prior to departure.

Several coronavirus cases have also been detected on flights arriving in Hong Kong from Mumbai, authorities said.

Densely populated Hong Kong was one of the first places to be hit by the coronavirus, but the tough entry conditions, strict social distancing measures and universal mask-wearing have helped keep infections to just over 11,700 with 209 deaths.

Around 9.8% of the city's 7.5 million population have been vaccinated so far.