The incident happened at Bray Lock, Amerden Lane, Taplow, close to the Berkshire border, at about 12:40 (local time), police said.
Two men and a woman, in their 40s, a woman in her 30s, a teenage girl and a three-year-old boy have been taken to hospital with non life-threatening injures.
Another man was treated for minor injuries at the scene.
The boat is believed to be privately owned and there were a number of adults and children on board at the time of the explosion, Thames Valley Police said.
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"A family had hired our vessel the Sandringham Lady for a party, and they heard the explosion and saw the smoke. They went over and helped the injured people off their boat and on to ours," he said.
"That boat effectively became an ambulance boat and they tended to the injured until the emergency services arrived," he said.
Thames Valley Police said officers were investigating to establish the circumstances of the explosion.