This route is known locally as the Golden Route because of the amount of traffiic it carries. As direct air links betwen Taiwan and mainland China are still banned, a lot of travellers route via Hong Kong.
According to IATA, the route carried 4.7miilion passengers in 200, double the second busiest route between SG and KL.
Cathay Pacific and China Ailines between them do over 80% of the flights. CX does around 15 flights a day.
Local news media is now reporting that at least one body has been recovered from the water.
Condolences too all involved.