The survivor is "very sick" and has been hospitalized, said Thai police spokesman Lt. General Prawut Thavornsiri. Police have not been able to interview the survivor yet and aren't sure of his nationality, but they believe he is Burmese.
Thai authorities learned about the camp from a suspect who tipped them off, Thavornsiri said. He would not say whether that suspect was linked with human trafficking.
"It is still under investigation," Thavornsiri said. "I can't reveal much information yet."
Some of the remains are in an advanced state of decay, so authorities have been unable to confirm identities or nationalities.
"We think there may be between 30-40 graves," he said. "The detention camp is situated on the Thai side near the Malaysian border. We have cordoned off the area, and will dispatch a team of forensic experts from Bangkok to the area tomorrow."
The advocacy group Human Rights Watch said the dead are Rohingya Muslims from Myanmar
or Bangladesh. In a statement released Friday, HRW cited police reports that say the victims "starved to death or died of disease while being held by traffickers who were awaiting payment of ransoms."
Some of the remains were found in shallow graves, while others were found in the open, covered only by blankets or clothes, the HRW statement said. It also claimed the camp was discovered in the Sadao district of Songkhla provice by a joint military-police task force.
That region is known to be a hot-spot for human trafficking, particularly of individuals coming from Myanmar.
"The finding of a mass grave at a trafficking camp sadly comes as little surprise," HRW Asia Director Brad Adams said in the statement. "Trafficking of persons in Thailand has long been out of control, something that senior officials have admitted to HRW and others."
Last year, the U.S. State Department downgraded Thailand to the worst possible ranking -- tier 3 -- in its Trafficking in Persons (TIP) report. It said Thailand is a source, a transit point and a destination for trafficking. The report also said that ethnic minorities and citizens of neighboring countries were especially at risk of exploitation in Thailand through forced labor or the sex trade.
The fate of Rohingya Muslims was an area of particular concern for the State Department. The 2014 TIP report said the Rohingya are among those most vulnerable to trafficking. They are a stateless people who have been fleeing ethnic violence in Buddhist-majority Myanmar for years. The Rohingya usually arrive in southwestern Thailand by boat and travel from there to Malaysia, where they often work illegally.
In January 2014, Thai police found hundreds of Rohingya men, women and children in a camp in the same province and near the same town where the bodies were discovered Friday.