The ferry, licensed to carry 150 passengers, was carrying 200 people during the 30-minute trip when the vessel began having engine problems, the Bangkok Post reported.
Passengers rushed to the top level of the two-deck ferry, causing it to list to the side and capsize, the newspaper said.
One pump on the ferry failed during the incident, Phuketwan reported.
"Three Thais and three foreigners are dead," a police officer said.
Of the three tourists, two were Russian and one was Chinese, Phuketwan said.
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