By Michael Bristow
BBC News, Beijing
Kim Jong-il has to think about who will succeed him
North Korean leader Kim Jong-il is reportedly on a visit to China, where he is looking for economic and political support from his biggest ally, according to experts.
Economic assistance - trade, aid and investment - is desperately needed in North Korea, which cannot even provide enough food for its own people.
But political support is also vital for a country that could have to deal with a change in leadership sometime in the next few years.
With its own problems to deal with, China's main aim is to ensure North Korea remains stable, according to analyst Jin Canrong.
"What China wants is no trouble. It has no greater expectations than that," said Mr Jin, of the People's University of China in Beijing.
Finding out what Mr Kim wants from China is no easy task - even basic facts about the visit were shrouded in secrecy.
But it is no secret that the North's economy is in trouble.
A recent report published by the International Crisis Group (ICG) said UN sanctions, poor policy choices and dwindling sources of foreign cash had shaken the country.
China is crucial to North Korea's fight for economic survival, providing Pyongyang with food, fuel and much-needed investment.
It could also be trying to nudge North Korea towards economic reforms, similar to those China embarked on 30 years ago.
On this visit to China, Mr Kim is believed to have visited Dalian and Tianjin, two dynamic cities at the heart of the country's economic transformation.
Many experts believe Mr Kim will want Chinese backing for a plan to hand over power to his third, and youngest son, Kim Jong-un.
The 68-year-old North Korean leader is believed to be in poor health, as video footage of him in China appears to confirm.
"The transfer of power is the number one issue, money is number two and then the security situation," said Jin Canrong.
That final point relates to North Korea's nuclear weapons programme and its neighbours' attempts to get Pyongyang to abandon it.
Talks involving six nations - China, Japan, Russia, the United States and the two Koreas - have been going on since 2003, with no real progress.
Those talks broke down last year and, despite attempts to revive them, there is no sign that they will begin again soon.
"Even if they were to restart the talks it would just be another couple of years of futile negotiations," said Willy Lam, of the Chinese University of Hong Kong.
"In the meantime, it would give North Korea more time and opportunity to pursue its nuclear ambitions."
Whatever the reasons for the trip, the mere fact that it is taking place at all suggests China and North Korea want to strengthen their ties.
China might not be as close to the North as it once was, but it still remains its only real ally.