SEOUL • North Korea's sanctions-hit economy shrank last year by its largest margin since the country's devastating famine in the 1990s, South Korea's central bank said.

North Korea's gross domestic product contracted by 4.1 per cent last year in real terms, the worst since 1997 and the second consecutive year of decline after a 3.5 per cent fall in 2017, the South's Bank of Korea estimated yesterday.

North Korea does not disclose any statistics on its economy.

The South Korean central bank has been publishing its estimates since 1991, based on information from various sources, including the South's foreign trading agencies.

"Sanctions that were added and strengthened in 2017 had a severe impact as drought hurt the farming sector, which accounts for more than 20 per cent of output," Mr Park Yung-hwan, head of the Bank of Korea's National Accounts Coordination Team, told reporters.

North Korea's international trade fell 48.4 per cent in value last year as toughened international sanctions cut exports by nearly 90 per cent, the worst loss in shipments since the central bank started publishing data nearly 30 years ago.

Output in the mining sector shrank 17.8 per cent because of sanctions on exports of coal and minerals, while the agriculture, forestry and fisheries sector contracted by 1.8 per cent because of drought, it said.

North Korea's population was estimated at 25.13 million and annual income per head was estimated at US$1,298 (S$1,776).

"The economy couldn't but contract severely given the sanctions that North Korea is under," said Mr Benjamin Katzeff Silberstein, a North Korea economy expert with the US-based Stimson Centre.

"This suggests that there's been a massive increase in domestic use of coal ... This is such a crucial export commodity and now that very little of it is being sold abroad, as compared to normal years, domestic industry is probably getting financially doped by cheap energy at the moment given how much of production is still going on," he said.

The United States and South Korea say tightening international sanctions over North Korea's nuclear weapon and ballistic missile programmes have been instrumental in leader Kim Jong Un's decision to pursue denuclearisation talks with Washington.

The International Federation of Red Cross and Red Crescent Societies last week said rates of malnutrition and disease are increasing in North Korea as it faces a harvest that is half of what was expected.

Mr James Belgrave, an official at the United Nations' World Food Programme who visited North Korea in April, said recently that there had been a drop of up to 20 per cent in North Korea's wheat and barley production due to an early dry spell.

"The wheat and barley crops did look very dry and were visibly affected," he told Reuters.

North Korea lacks adequate agricultural infrastructure as well as farming techniques and fertilisers, and sporadic famines are common.

In the 1990s, a nationwide famine killed as many as one million people.

REUTERS