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 ($1,340) in the North last year, Statistics Korea said in statement, up five per cent.

It was the fastest expansion since 2011, when incomes rose by more than seven percent, a graph issued by Statistics Korea on Friday 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.