This is what the IATA site says......
https://www.iatatravelcentre.com/
TWOV (Transit Without Visa):
Nationals of Sri Lanka traveling on Cathay Pacific (CX) or Cathay Dragon (KA) are allowed to transit without a visa if passenger has a valid visa or proof of residency of Australia, Canada, Japan, Korea (Rep.), New Zealand, United Kingdom, USA or a Schengen Member State.
WARNING: A HKG Transit Visa is required when connecting with an airline other than Cathay Pacific (CX) or Cathay Dragon (KA).
a. Originated station makes passport photocopy for station filing in case required to submit to HK Immigration upon request.
b. Send MAAS telex – TWOV to arrival carrier for escort and keep departure carrier copied.
c. MAAS – TWOV telex MUST include the port of origin / destination, flights / date, passenger full name, passport numbers and date of birth.
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