Hong Kong health authorities are investigating a carbon monoxide poisoning incident involving a 31-year-old man, who lost consciousness and sustained a head injury after smoking shisha at a Mong Kok bar.

But Hubbly Bubbly, the bar in question, told the Post on Tuesday it stopped offering shisha in the middle of last year and saw no customers fainting recently. Authorities also conducted a spot check and did not identify any illegal smoking.

The Department of Health said it received a report from the United Christian Hospital about the incident.

“A 31-year-old man lost consciousness and hit his head due to carbon monoxide poisoning after smoking shisha last Friday,” a department spokesman said. “He regained consciousness and sought medical attention on his own and was discharged after treatment.

“Preliminary investigation suggested that the man was smoking shisha with charcoal fuel in a bar on that day, and the premise was windowless with its door closed.”

Smoking indoors is prohibited in Hong Kong, and offenders can be fined HK$1,500 (US$191).