Police Col. Thammanoon Mankong says the boat started to sink Friday about 100 meters (328 feet) from a pier in Pattaya.
He says the 27 South Korean tourists were rescued by authorities and crew from nearby boats. One of the tourists was slightly injured and taken to a hospital. The boat's crew members also were rescued.
The boat was returning from a trip to Lan Island, a popular getaway in the Gulf of Thailand, 7 kilometers (4.4 miles) west of Pattaya.
Pattaya is 100 kilometers (60 miles) southeast of Bangkok.