Recurring defections by staff from North Korean restaurants in China have thrown the spotlight on these establishments, one of Pyongyang's discreet ways of earning foreign exchange.

These restaurants are served by several waitresses, female chefs and interpreters, their uniforms redolent of the ones worn by members of the Moranbong, North Korea's all-female pop band, well-known for its odes to leader Kim Jong-un and unofficially known as 'Kim Jong-un's girls.'

The latest case of defections came to light on Wednesday, after three workers from one of these restaurants in China's northwestern province of Shanxi fled to South Korea.

In April, the manager and 12 waitresses from a Ningbo restaurant in eastern China also defected to South Korea, while in May two or three other restaurant workers fled to the South.

The defections have grabbed attention for various reasons, particularly that the restaurant workers are chosen based on apparent loyalty to the regime, and according to South Korea, the employees usually hail from families connected to North Korea's ruling elite.

The other reason is China's reluctance to oppose the passage of defectors to South Korea - usually through a third country such as Thailand or Vietnam - if they possess valid travel documents.

The defection of the 13 people angered the North Korean authorities, who alleged they were abducted and demanded their repatriation in vain.

North Korean restaurants abroad are one of the communist state's tools to earn forex, especially as it reels from fresh international sanctions following its January nuclear test, and their adverse impact on trade, including with China, a traditional ally.

Following Pyongyang's atomic test, Seoul asked its citizens to boycott these establishments to avoid funding the enemy regime.

However, both China and North Korea refuse to supply figures on how many of these restaurants are in operation, although according to Seoul the Kim regime runs around 130 restaurants across 12 countries - mostly in China - earning it around $10 million annually.

A quick search throws up at least eight such diners in Beijing, one of the most popular being adjacent to the North Korean embassy, whose waitresses - all young - reside inside the diplomatic mission complex.

It is common to see them commuting between both buildings, accompanied by male guards, seemingly to prevent them straying from the set route.

The restaurants offer typical Korean dishes, each table supplied with a barbecue so customers can grill the meat to their liking, besides pickled vegetables, 'kimchi' - fermented cauliflower - or seafood and other grilled delicacies.

Beverages include North Korean beer brand Taedonggang and soju, a liquor similar to the Japanese 'sake' but with a touch of ginseng.

The menu also offers items bound to horrify the regular Western or non-Oriental tourist, including dog soup, meat or ribs, and 'soup of longevity' containing snapping turtle.

Some of the restaurants have stages for musical acts by female performers, moving to the sounds of traditional instruments and even drums, saxophone and electric guitar.

The staff are impeccably turned out and polite, although it is nearly impossible to engage them in conversation beyond their professional duties.

One waitress indicates that she also speaks Russian and has been in China for under a year, in which time she has not ventured out of the city.