Record-breaking Hong Kong and Australia swimmer Kenneth To has died suddenly aged 26 after falling unwell at a Florida training camp, officials said on Tuesday.
To won Commonwealth gold and world silver medals before switching from representing Australia to his native Hong Kong, for whom he held 16 records.
The Hong Kong Sports Institute said To was on a three-month training programme at the University of Florida when he passed away.
"He felt unwell at a training session and was taken to hospital where sadly, he passed away," a statement said, adding that the Institute was "deeply shocked and saddened".
"He was extremely popular and loved by his teammates and competitors. Kenneth was known as a truly exceptional person, warm, funny and kind. His sudden passing is a huge loss to local sports."
The South China Morning Post said To, who was born in Hong Kong but raised in Australia, felt unwell in the locker room after a training session.
To was part of the Australian teams that won Commonwealth gold in the 4x100m freestyle relay in 2014, and silver in the 4x100m medley relay at the 2013 world championships.
He shifted to represent Hong Kong in 2016, but remains the Australian short-course record-holder in the 100m and 200m individual medley.
"I still can't accept the news of his death, it's so shocking," Hong Kong swimmer Yvette Kong told the Apple Daily newspaper.
"He made a lot of contributions to the Hong Kong swimming world. It is such a pity."