Nethersole Hospital said a 79-year-old patient died one day after tissue was found in his throat.
The hospital in Tai Po said the chronically ill patient had been in stable condition after he was admitted on Friday, until he suffered a cardiac arrest on Monday morning.
It was during resuscitation that medical workers found the tissue in his throat.
His heartbeat was restored after being intubated, but his condition deteriorated and died on Tuesday.
His case has been reported to the police and passed onto the coroner for further investigation.