Police were informed of the incident, some 10 minutes’ boat ride offshore, at 5:20pm.
Rescue teams were dispatched to AA Marina Pier in Rassada while other boats rendered assistance.
All seven passengers were safely brought to shore, while three boat operators stayed behind in an attempt to right the overturned vessel.
The passengers, a family of seven (six Thai nationals and one man with dual British and Taiwanese citizenship), were transported to Bangkok Hospital Phuket.
Four passengers were uninjured, while the other three sustained minor abrasions. None required hospital admission.
The rescue operation took about one hour, police noted in their report.
Passengers told police that the boat was travelling at a safe speed when it began to tilt and eventually capsized, police presumed due to high waves.
The longtail boat was eventually towed to Tambon Phru Nai on Koh Yao Yai.
Police are still investigating the exact cause of the incident.