Six Chinese nationals and one American citizen have been detained after admitting having been hired to do a standardised college admissions test for other people in Thailand.

The seven people identified at Monday's press conference are Chinese nationals Wang Jie, 27, Lin Jia, 28, Chen Juan, 33, Huang Li, 27, He Liu, 28, Huang Xiaofan, 39, and US citizen Michael Li Yao, 30.

The Technology Crime Suppression Division (TCSD) was contacted on Friday by an institution that organises the American College Testing (ACT) exam in Thailand, which asked for help in investigating irregularities with a number of test applicants, Immigration Bureau chief Surachate Hakparn said.

The exam was carried out at Mahidol University's Nakhon Pathom campus on Friday.

The TCSD found that a Chinese national had paid the test fees for several applicants using the same credit card, said Pol Lt Gen Surachate.

Officials then questioned Mr Wang, Ms Lin, Ms Chen, Ms Huang and Mr Yao for more information about the payments, he said.

During questioning, all the suspects failed to confirm their personal information as listed in their passports, forcing the TCSD to seek help from immigration police in Nakhon Pathom to verify their identities.

The five applicants were then arrested.

Later on Saturday, the TCSD was again contacted by the organiser, who requested more assistance to investigate similar irregularities it found during a test conducted at NIST International School in Watthana district of Bangkok, he said.

Mr He and Mr Huang failed to answer questions relating to their personal information as detailed in the passports they used, so they were also detained.

All of the detained suspects later admitted to using fake passports to sit the test and that they were hired to sit the exam for someone else.

The suspects used their genuine passports when they entered Thailand for these tests; but they used fake passports with their pictures to sit for the exams on Friday and Saturday, he said.

Each suspect were promised a payment of between 40,000 to 90,000 baht each upon their return to China, had they not been detained.

Mr He had in his possession eight fake passports, and he admitted to having sat for the ACT exam for other people who reside in other countries in the past.

All suspects have been charged with falsifying a travel document and possessing fake passports. Meanwhile, Mr He faces an additional charge of possessing fake passports with the intent to distribute.