Bus driver Preecha Ramwong, 40, said he swerved to avoid hitting another vehicle Thursday and went into a roll in a rice field.
"I was traveling at a low speed," he said.
The bus was carrying 51 passengers at the time of the accident, though it wasn't clear if all of them were Russian nationals, RIA Novosti reported. The tourists were en route to an elephant-trekking tour.
Three Russian women were in intensive care at an area hospital following the accident, Phuketwan reported.