North Korea has completely cut off state food rations after China failed to supply the impoverished communist country with extra cereals, a welfare group said Monday.

The ruling communist party announced in a directive on May 26 that there would be no state rations for a while, said South Korea's Good Friends group which has contacts in the North.

People were authorised to buy food supplies through private markets, it said, adding the directive was due to delayed shipments of food from China.

"The directive was unavoidable" because China failed to send the aid which had been anticipated after leader Kim Jong-Il's trip to Beijing in early May, group president Pomnyun, who uses just one name, told reporters.

Private markets are now open around the clock across the North, he said.

The North suffered famine in the mid-1990s which killed hundreds of thousands and it still grapples with severe food shortages. The UN children's fund estimates one third of children are stunted by malnutrition.

The state food distribution system collapsed during the famine. Free markets sprang up and were condoned for a time.

Since 2005 the regime has been reasserting its grip on the economy, with controls or outright bans on the private markets.

A currency revaluation last November, designed to flush out entrepreneurs' savings, backfired disastrously, fuelling food shortages as market trading dried up and sparking rare outbreaks of unrest.

The North was forced to suspend its campaign to curb the private markets.