Thai police have detained 175 North Koreans in a raid on a house in suburban Bangkok.
The North Koreans were picked up after a tip-off
It is the largest group of North Koreans ever suspected of illegally entering Thailand, officials say.
The group, most of them women and children, will be charged with illegal entry and face possible deportation to a third country, according to police.
Tens of thousands of North Koreans have tried to leave their country in recent years, fleeing hunger and repression.
They often seek asylum at the embassies of third countries, but many are thought to be in hiding in South East Asia.
Officers raided the house late on Tuesday night, after receiving a tip-off from neighbours.
They found a total of 45 males and 130 females inside the building in Bangkok's Huay Kwang district. Twenty-five of the group were children.
N Koreans seeking asylum often target foreign embassies
Of these people, 16 had already been processed by the United Nations High Commissioner for Refugees, and were soon due to leave Thailand for South Korea.
The other 159 are thought to have no documents, but are also reportedly seeking asylum.
"This is the biggest single arrest of North Koreans" in Thailand, Police Major General Pramoj Pathumwong told Reuters news agency.
Most North Koreans who manage to leave their impoverished homeland travel across the border to a region of north-east China populated by ethnic Koreans, but they face repatriation if caught by the Chinese authorities.
Some then manage to cross China to reach South East Asia, where they have the chance of being sent on to South Korea. Most of these transfers are done outside the public gaze, to avoid confrontations with Pyongyang.
But on rare occasions, these transfers become public knowledge. In July 2004, more than 460 refugees arrived in South Korea on a special flight from an unnamed third country, thought by analysts to be Vietnam.
There have also been many cases of North Koreans targeting foreign embassies in China, in the hope of seeking asylum.