North Korea's state media reported Sunday an "unimaginable" accident at an apartment construction site in Pyongyang, which had resulted in an unspecified number of casualties.
South Korean officials said the incident involved the collapse of a 23-storey apartment building, which already had close to 100 families in residence.
It is extremely rare for North Korea to report negative news of this type, and the despatch from the official KCNA news agency included equally rare apologies from top officials.
KCNA said the accident had occurred last Tuesday and was the result of "irresponsible" supervision by officials in charge of the construction.
An "intensive" emergency rescue effort had been carried out to rescue survivors and treat the wounded, it said.
The KCNA did not provide a death toll or elaborate on the cause of the collapse, but said it had left Pyongyang citizens "greatly shocked".
The agency carried lengthy public apologies by senior officials including the Minister of People's Security, Choe Pu-Il.
"(Choe) repented of himself, saying that he failed to find out factors that can put at risk the lives and properties of the people and to take thorough-going measures, thereby causing an unimaginable accident," it said.
Kim 'up all night, feeling painful'
A South Korean official, speaking on condition of anonymity, said Seoul was aware of the incident which involved the collapse of a 23-storey apartment complex.
"It is common in North Korea that people move into a new apartment building before construction officially ends," the official told AFP.
The official said 92 families were believed to be living in the collapsed building, and the final death toll was likely to be "considerable".
The North's leader Kim Jong-Un "sat up all night, feeling painful" after being told about the accident, according to a senior Pyongyang official quoted by the KCNA.
The young leader "instructed leading officials of the party, state and the army to rush to the scene, putting aside all other affairs and command the rescue operation," Kim Su-Gil, chief secretary of the city committee of the ruling Workers' Party, said in his public apology.
All Pyongyang citizens were "sharing sorrow" with the bereaved families and victims, the official said, calling all to "overcome sorrow with courage".
About 2.5 million people -- mostly political elites including senior party members or those with privileged background -- are believed to live in Pyongyang.
Pyongyang residents are known to enjoy better access to electricity, food, goods and other services than those living elsewhere in the impoverished and isolated country.
The secretive nation has rarely made public the details -- especially death tolls -- of major accidents.
But in one exceptional case, the North announced in April 2004 a massive train explosion in the northwestern county of Ryongchon had left 154 -- including dozens of schoolchildren -- dead and some 1,300 injured.
The accident -- caused by damaged electric wires -- devastated many nearby towns, prompting Pyongyang to make a rare plea for help from the international community.
The North is under layers of UN sanctions imposed after its disputed nuclear and missile tests, and suffers chronic shortages in food to fuel and medical supplies.