North Korean refugees reluctantly taken by the South

The BBC has an article on this, reporting North Korea's bizarre claim that South Korea has kidnapped the refugees.

N Korea condemns refugee move

North Korean defector aboard coach after his arrival in the South
The refugees are thought to have escaped through China and Vietnam
A spokesman for North Korea has accused the South of kidnapping its citizens after more than 450 defectors arrived by plane in the space of two days.

The refugees began arriving from an unspecified country on Tuesday on planes chartered by the South, in an operation shrouded in secrecy.

All had apparently escaped through China to the unnamed third country.

"This is an organised and planned kidnapping as well as a terror crime," North Korea's spokesman said.

The fact is that the South Korean government is far from keen to take North Korean refugees - it upsets the regime in the north and it costs money to support them: they get some $20,000 on arrival, plus monthly stipends until they are able to find work, which apparently takes a long time.
The border between the Koreas is highly militarised, with millions of North and South Korean troops (and 15,000 Americans) facing each other over the DMZ, so refugees generally can't get through that way. Many escape through the long land border with China but in recent years this has become very hard since the Chinese government refuses to recognise them as refugees and captures and returns many, in contravention of international law, even going as far as grabbing North Koreans as they try to enter the premises of the South Korean embassy in Beijing.
Still, many do escape through China to other countries, mainly in South East Asia. They then arrange flights to South Korea, typically arriving individually or in small groups. The recent arrival of more than 450 refugees in two groups is unusual, and suggests pressure has been put on South Korea by the South East Asian government in question - unofficially known to be Vietnam.