'Cases have now increased for the ninth straight week' said the Director General of the WHO, as the COVID-19 pandemic continues to intensify around the globe.
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Experts are working to understand how dozens of passengers on a flight from Delhi tested positive for COVID-19 on arrival, despite them all testing negative before boarding.
At least 52 passengers returned positive tests after flight UK6395, operated by Indian airline Vistara, landed in Hong Kong on 4 April .
They had all tested negative before the flight, as Hong Kong only allows entry to travellers who return a negative pre-flight test from a reputable lab with 72 hours of departure.
Six passengers had been denied boarding because the standard of their test result wasn't up to scratch, the Wall Street Journal reported.
Despite the rigorous screening, eight positive cases were detected before passengers began Hong Kong's three weeks of mandatory hotel quarantine, while the others were picked up during the quarantine period.
There were 146 adult passengers and seven children on the Vistara charter flight, which was organised by Hong Kong travel company Nanda Travel to return stranded travellers from India.
"We're shocked by this," the company's director Poonam Nanda told the Journal.
"This one flight appears to be an astonishing outlier and we are all confounded by these numbers."
Passenger Rashida Fathima, who was on the flight with her husband and two children, told the Journal she believed the caught the virus on the plane, despite wearing a face mask for most of the six-hour journey.
She said some passengers were coughing during the flight and many took off their masks to eat prepackaged meals, which was allowed.
Hand sanitiser and alcohol wipes were available on board.
Vistara said it ensured "strict compliance with all guidelines issued by the Indian as well as the destination countries' authorities for all flights".
Hong Kong has now suspended all flights from India until May 3 at least. Australian authorities are considering today a similar move as the spread of COVID-19 escalates in India.
With air travel considered by experts to be reasonably safe, health experts have cited a number of possible reasons for why 52 passengers came to test positive after the flight, including the transmission of a more virulent strain of the virus.
University of Hong Kong scientists are sequencing genomes from the passenger cluster as part of investigations into whether they were infected on board.
Experts say passengers could have become infected in India between returning a negative test and boarding the flight, and that results could have been false negatives.
They are also considering whether the passengers became infected in Hong Kong's quarantine hotels, rather than on the plane.
Epidemiologist Eric Feigl-Ding from the Federation of American Scientists pointed to recent cross-transmission in hotel quarantine in Australia to show quarantine transmission was possible.
"Some may have occurred after the initial 72 hour pre-departure time window after they got tested. India cases increased 60 per cent each week for the last two weeks. But this is why our border testing is leaky," he tweeted.
4) to be clear, it possible not all transmission occurred during the flight. Some may have occurred after the initial 72 hour pre departure time window after they got tested. India cases increased 60% each week for the last 2 weeks. But this is why our border testing is leaky. pic.twitter.com/7aGsVLqQ6a
"So, it could also be hotel transmission to some degree too," he added. "Hotel room cross infections have been observed in Australia's hotel quarantine system too.
"Regardless, the epidemic situation from India is too hot."
Western Australian premier Mark McGowan has said Covid-19 tests conducted in India for people returning to Australia "aren't accurate or aren't believable" as the Federal Government considers a suspension of flights from the country.
The National Security Committee of cabinet, led by Australian Prime Minister Scott Morrison announced Australia would join New Zealand in banning international arrivals from India.
McGowan has backed an anticipated flight ban by the security committee, as he warned of a "significant" rise in cases after 78 of the 79 passengers on a flight to Perth on Saturday had been in India recently.
"It's obviously a diabolic situation that is going on in India at the moment, but it does put extreme pressure on our systems here in Western Australia and indeed in other states," he said.
"I'm advised that other states are going through exactly the same experience.
"We obviously have a problem with India," he added. "Some of the tests conducted in India either aren't accurate or aren't believable and clearly that's causing some issues here."
On Monday, India recorded another day of record coronavirus figures, with 352,991 new infections and 2812 deaths.
