A rule banning spectators from bringing water bottles into competition venues at Kai Tak Sports Park should be relaxed to reduce waste, a green group said, after noticing exemptions were given to certain guests.

Greenpeace campaigner Leanne Tam told RTHK on Sunday that during the World Snooker Grand Prix at Kai Tak Arena, a VIP ticket holder was seen using their own bottle, an otherwise prohibited item for the general audience.

She added that other spectators from the VIP section were even handed bottled water, generating unnecessary waste.

"I do think that their security problem is the most important issue. When the Kai Tak Sports Park keep [repeating] that you cannot bring your own bottle and water bottle is not safe enough, but you can see that in the venue, the event organiser will freely distribute the plastic water bottle [with a] cap," she said.

"I think actually there's no so-called safety issue in that situation because in the whole event, I can feel that it's so safe. It doesn't become dangerous when the VIP have their water bottle in their seats."

Tam suggested that if water bottles are indeed considered a safety risk, the park should immediately introduce a reusable cup regime.

"If...the organiser really wants to keep their balance between the safety and user experience and also the environmental protection issue, we suggest that they should have a reusable cup service to all the guests in the venue," she urged.

"You can freely use it to fill water in your own cup and it's safe because it's without a cap, and it's purchased by the venue so it's under the safety regulations."

The environmental campaigner added that the idea had been implemented before, including the Rugby Sevens at Hong Kong Stadium.

Similar venues overseas also provide a reusable option for attendees, she noted, and Kai Tak Sports Park should be able to follow suit.