Ninety-nine people including migrant workers from neighbouring countries were arrested for overstaying their visas during coordinated raids on 118 locations across the country yesterday.
Most of the suspects are from Myanmar, Laos, India, Germany and African countries.
All were charged with entering the kingdom illegally and overstaying.
The raids were part of an operation called X-Ray Outlaw Foreigner. They were jointly conducted by the Narcotics Suppression Bureau, the Central Investigation Bureau, the Immigration Bureau, the Tourist Police Bureau, the Patrol and Special Operation Division and local police.
Tourist Police deputy commissioner Surachate Hakparn said the raids included tourist-heavy spots like Pattaya in Chon Buri, Songkhla's Hat Yai district and the resort island of Koh Samui in Surat Thani.
Searches were also conducted at 74 international schools, where a number of Africans had been hired as teachers and were still teaching despite the fact their visas had expired, he said.
Pol Maj Gen Surachate sought cooperation from education institutes and entreated them to avoid helping foreigners change their tourist visa to a student visa by granting them certificates, which he said was illegal as it violates the nation's immigration law.
Regarding non-Thais who may work for transnational crime syndicates, Pol Maj Gen Surachate said an investigation indicated that most credit card scams are perpetrated from African countries like Nigeria and Guinea.
He said the investigation also showed that Africans were the most likely to be trafficking narcotics.
Some of the suspects had 300,000-400,000 baht circulating in their bank accounts but were unable to clarify where it came from. he added.
Authorities also detained Ezeocha Nnamdilucky, a 35-year-old Nigerian, in Bangkok's Prawet district.
The suspect has been wanted by the Criminal Court since April 10 for allegedly possessing cocaine with intent to sell.
Mr Nnamdilucky was being held at the condominium he was living in on Chalerm Prakiat Rama IX road.
He said security personnel had been tipped off by an informant. They then staked out his apartment and confronted him.
Mr Nnamdilucky held a non-immigrant visa, meaning he was entitled to stay in Thailand for 90 days. This type of visa is usually granted to foreigners who have families here.
In a bid to prevent them from repeating similar offences, Pol Maj Gen Surachate said DNA samples would be collected shortly so their biological information could be incorporated into the country's criminal database.
They would also be blacklisted and extradited to their home countries, he said.
According to Pol Maj Gen Surachate, more than 4,000 foreign suspects have been apprehended during 1,024 operations, resulting in a decrease in transnational crime in Bangkok.
Seventy-five foreigners were detained for overstaying or working illegally in similar raids across the country at the end of February.