The vessel sank during an early-morning tour at Horizontal Falls, off Australia's Kimberley coast.
Local media reports state that 26 passengers and two crew members were on the boat when it went down.
West Kimberley Shire president Geoff Haerewa said the vessel hit rocks at the world-renowned beauty spot.
Injured passengers have reportedly been airlifted to hospital in the town of Broome, around 155 miles away.
Police say none of the injuries are life-threatening.
A Western Australia Health Service spokeswoman said: "Kimberley Hospitals are on stand-by and Broome Health Campus has activated an emergency alert in anticipation of patient arrivals – the first of which are expected within the hour."
Broome Police tweeted: "Kimberley Police are dealing with an ongoing incident at Horizontal Falls. Several persons have been injured but no injuries are believed to be life threatening."
Horizontal Falls Seaplane Adventures, which has flown some of the injured passengers to Broome, said: "Falls Express, guided by an experienced skipper during an early-morning tour, was involved in the incident while travelling through the falls.
"The vessel immediately returned to the pontoon. [We] are continuing to liaise with the RFDS and emergency services to manage the incident."
The incident took place near Australia's Horizontal Falls
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Broome, Australia
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