North Koreans enjoyed the fastest improvement in their incomes for five years in 2016, Seoul's statistics agency has said - but Southerners are still more than 20 times better off.

Per capita incomes averaged 1.46 million won (US$1,340) in the North last year, Statistics Korea said in statement, up 5 per cent.

It was the fastest expansion since 2011, when incomes rose by more than 7 per cent, a graph issued by Statistics Korea on Friday (Dec 15) showed, and came despite the imposition of multiple sets of international sanctions over Pyongyang's nuclear weapons programme.

The isolated North is one of the world's most secretive countries and does not release official economic data, not even for GDP growth, leaving observers to compile estimates of their own.

In the capitalist, democratic South, the comparable per-capita income figure was 31.98 million won - nearly 22 times higher.

Other comparisons issued by Statistics Korea also put the South far ahead.

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Its electricity production stood a 540.4 billion kilowatt hours in 2016, the agency said - almost 23 times the North's 23.9 billion kilowatt hours.

Mobile phone subscriptions were 14.26 per 100 people in the North, and 122.65 in the hyper-wired South - more than one per person.

South Korea's total trade volume was put at $902 billion, almost 140 times the North's $6.5 billion.

In July the South's central bank estimated the North's GDP to have grown 3.9 per cent last year - faster that the South's 2.8 per cent, albeit from a much lower base.

It was the North's fastest expansion for 17 years as Pyongyang quietly allows the market to play a greater role in its economy under Kim Jong-Un, even while denying it is carrying out reforms.

"Marketplaces are a key pillar for growth in the North Korea as many people are now relying on such markets for their incomes instead of the country's dysfunctional rationing system," said Hong Min, a senior researcher with the state-run Korea Institute for National Unification.

Statistics Korea put the North's 2016 population at 24.9 million, compared with 51.3 million in the South.