The ferry, called “Koh Yao”, departed for Koh Yao Yai at 2pm, Phuket Marine Office Director Wiwat Chitchertwong told The Phuket News.
The accident occurred at about 3pm while the ferry was returning to Phuket, he added.
“There was nothing to prevent the vehicle from falling into the water. The owner of the truck did not apply the handbrake, and there were no tethers to prevent the truck from moving,” Mr Wiwat said.
“The owner was not in the truck when it fell, so he was safe,” he added.
The boat has been impounded and taken to Jian Wanit Pier in Rassada to be inspected by officials, Mr Wiwat said.
“The ferry boat owner will buy a new vehicle for the truck owner and be responsible for recovering the sunken pickup from the water,” Mr Wiwat assured.
“I have already ordered the ferry boat operator to place a buoy at the location where the truck sank,” he said.
“I ask all local local fisherman and tour operators to avoid the area until the truck is removed for safety,” Mr Wiwat added.
Additional reporting by Eakkapop Thongtub