* Qatar Airways to pay $661mn for stake
* Joins concentrated register alongside Swire Pacific, Air China
* Qatar Airways also owns stakes in IAG, LATAM, Meridiana

Qatar Airways said on Monday it had broadened its global reach with the acquisition of a 9.61% stake in Cathay Pacific Airways Ltd, complicating the Hong Kong carrier's share registry and sparking a sharp fall in its share price.
Hong Kong's Kingboard Chemical Holdings said it had sold the stake to Qatar Airways for HK$5.16bn ($661mn), making the Middle Eastern carrier the third-largest shareholder in Cathay.
For Cathay, the Qatar stake will give it a third strategic shareholder behind Swire Pacific Ltd and Air China Ltd , potentially complicating a restructuring plan aimed at slashing HK$4bn in costs over three years.
Without domestic flights to underpin earnings, Asian carriers Cathay and Singapore Airlines Ltd have struggled against Chinese and Middle Eastern rivals, with Cathay already shedding 600 jobs since May.
For Qatar Airways, its first major stake in an Asian airline will allow it to boost its global influence and potentially traffic through its Doha hub, amid the crisis among the Gulf states.
The airline has been unable to fly to the previously lucrative markets of the United Arab Emirates and Saudi Arabia as part of an airspace rights dispute with neighbours, and has been looking to invest elsewhere to broaden its reach.
It was rebuffed by American Airlines Group Inc earlier this year.
Despite Cathay's troubles, Qatar Airways Chief Executive Akbar al-Baker described it as "one of the strongest airlines in the world ... with massive potential for the future".
Cathay shares have risen by 29.4% since the start of January despite the airline in August posting its worst first-half loss in 20 years.
Shares of Cathay Pacific dropped as much as 4.7% on Monday morning, as investors worried about its direction with Qatar Airways on its registry. The stock was 1.7% down at 0342 GMT, while the broader market was down 1%.
"Cathay will have three major shareholders, all with different and potentially conflicting interests - Swire, Air China and Qatar Airways," said Corrine Png, CEO of transport research firm Crucial Perspective.
"This may not necessarily be favourable for Cathay as it is facing operating challenges and undergoing transformation."
Swire Pacific owns 45% of Cathay and Air China 30%.
Cathay flew between Hong Kong and Qatar Airway's Doha hub as part of a codeshare arrangement between 2014 and 2016, when the route was axed "for commercial reasons".
Qatar Airways' investment strategy has seen it acquire 20% of British Airways-parent International Consolidated Airlines Group, 10% of South America's LATAM Airlines Group SA and 49% of Italy's Meridiana.
Investment holding company Kingboard said it would recognise a gain of HK$800mn on the sale of its entire Cathay stake.