The bus driver told police he ran off the road and struck a pole to avoid another vehicle. ''I was travelling at low speed,'' said Preecha Ramwong, 40.
The bus, carrying 51 tourists, left the road and crashed in the Bung district of Chonburi province, where Pattaya is located, about 6.30am.
Police were told the tourists to Thailand were on their way to Kanchanaburi province for a day of elephant trekking and other activities. Nearly all of them were still asleep when the bus crashed.
It hit the pole and ended up in a rice field, officers said.
The crash is the latest in a series of mishaps in Thailand that have killed or injured tourists, Russians among them.
Seven tourists were killed when a ferry returning to Pattaya from Lan island capsized earlier this month. A Russian boy became the final victim when he succumbed to his injuries in hospital.
Envoys from several countries have grown increasingly alarmed at the numbers of tourists who drown or are involved in serious road crashes while holidaying in Thailand.
In intensive care today were Mrs Galina Katorova, 59, Mrs Anzhelika Sotnikova, 39, and Miss Nadezda Anokhova, 35.
The other tourists injured in today's crash have been named as Gary Pomeransev, 75, Tatiana Dolgintceva, 27, Larisa Bolshova, 52, Andrey Sivoplias, 35, Maksim (no surname) 7, Misha Anokhon, 12, Alexsandr Kartkev, 35, Valeriia Sotnikova, 20, and Kristina Khomenko, 25.
Phuket has also had several incidents involving tourists but with less serious outcomes.
Scores of international students from Bangkok were injured when a bus rolled backwards and crashed on Phuket's Patong Hill last weekend.