The United States should consider negotiating a separation line with China in a collapsed North Korea, a study said Thursday, warning of catastrophic consequences if Kim Jong-Un's regime suddenly falls.

The report by Rand Corp., a prominent US research institute, said that the crumbling of the totalitarian state could trigger a new, severe famine as well as a human rights crisis in a country that holds hundreds of thousands of prisoners.

The United States and its ally South Korea would almost certainly intervene, causing alarm in China, which is North Korea's primary ally, the study said.

China, whose perceived interests include stemming the flow of refugees and preventing US forces from approaching its border, could also send troops into North Korea and risk a confrontation with US or South Korean forces that could quickly escalate, the report said.

"The best way to minimize such accidents is to define a separation line for Chinese forces versus (South Korean) and US forces," the study said.

The line could be as far north as 50 kilometers (30 miles) into North Korea from the Chinese border or as far south as the capital Pyongyang, it said.

Bruce Bennett, the author of the study, acknowledged that the idea would be unpopular in South Korea and evoke the division of Germany after World War II.

The Korean peninsula itself has remained split since the 1950-53 war that pitted the United States and its Western allies against a pre-industrial China.

"Establishing a line like that is really not a good idea -- it's politically bad -- but on the other hand, having a war with China is even worse, I think," Bennett said.

"And so ultimately we may have to create a line that says the Chinese won't go south, we won't go north," he said.

The United States and South Korea should coordinate with China on key priorities such as bringing food into North Korea and securing the country's nuclear and other weapons of mass destruction, the study said.

China, which may seek to support a faction of the former North Korean regime, should agree to withdraw forces eventually and allow reunification, likely under the auspices of a UN Security Council resolution, the Rand report said.

But UN resolutions can take time and it would be "far preferable" to agree with China on guidelines ahead of a North Korean collapse, it said.

Bennett said he researched the report due to concern that the key countries had not spoken enough to each other about what to do if the impoverished state implodes.

"Maybe the probability of a North Korean collapse in the next year is two percent. That's a dangerous two percent," he said.

"What's the probability that your house burns? It's probably not two percent, it's a lot less, but do you have fire insurance? I do," he said.

The study did not try to predict a time for a North Korean collapse but expected the regime would fall eventually.

One of the likeliest scenarios for a collapse, according to the study, would be an assassination of Kim Jong-Un.

Kim, who replaced his late father Kim Jong-Il in December 2011, is believed to be in his late 20s and has not designated a successor.

The sudden loss of a central leader could lead to factions running North Korea, bringing anarchy and severely impeding food distribution, the study said.

Hundreds of thousands of North Koreans starved to death in the mid-1990s after the break-up of the Soviet Union ended a key source of aid.