Waiting for the customs office on the Chinese side to open, a local couple in their thirties were trussing up heavy cartons and bags to carry across the border. "All the other North Korean relatives of the Chinese Koreans around here have written letters saying no one has anything to eat," explained the man. So he and his wife were taking provisions to his aunt: "Grain and other foodstuffs ... all food." China now limits the amount of grain which relatives can take across to 100kg. "But that is not enough, so sometimes we must go through the `back door' to take more," said another Chinese Korean woman.
Following disastrous flooding in 1995 and 1996, North Korea is in the grip of severe malnutrition, and may be on the brink of widespread famine. Begging letters arrive regularly in this corner of north-east China, the Yanbian Korean Autonomous Prefecture, where 40 per cent of the 2 million population are ethnic Koreans, the result of population migration between the late-19th century and 1945.
Many Yanbian Chinese Koreans here have relatives in North Korea; one local government official said he had received 15 letters from his cousin asking for help. These increasingly desperate missives provide one of the few channels of regular information out of the closed Communist state. While the border is shut to foreigners, Chinese can cross from Yanbian to North Korea with just a permit, laden with food for starving relatives - or sometimes with a more commercial approach to China's hungry neighbour.
In Tumen's market, second-hand Chinese clothes are on sale for locals to buy for relatives. And for anyone interested in North Korean souvenirs, the stalls offer traditional stone soup pots, metal cooking pans, brass chopsticks and large stuffed birds - the few North Korean products still manufactured. Some of the soup pots are well-used. "They are selling their old pots, just to have enough to eat," said a stallholder.
One truck parked in front of the Tumen customs building had rumbled back into China piled with bulging sacks. The driver was from Heilongjiang province, China, where the last harvest was so bountiful that "the peasants could not sell everything, so they thought about selling to North Korea". He had taken a truckload of wheat flour and bartered it for medicinal Korean herbs. How did the North Koreans look? "I heard that people died of hunger ... everyone is very thin." The driver pointed out that he himself was rather fat. "In North Korea I seem like I am an exploiter," he said.
There was a time when trucks passed frequently along the long, narrow bridge across the Tumen river, one of seven border crossings from Yanbian. But the economic woes of the "hermit kingdom" have resulted in a spectacular collapse in the value of trade between Yanbian and North Korea, from a peak of $300m (pounds 190m) in 1993 to just $17m last year, said Huang Denan, director of Border Trade Management at the Yanbian Foreign Trade and Economic Co-operation Bureau. "North Korea has almost nothing to provide ... Most border trade is barter trade, so if one side has nothing to supply...", he shrugged. North Korean state enterprises at present owe about $10m in bad debts to Yanbian trading companies.
North Korea can just about still supply some wood, fertiliser, scrap metal (including old railway track) and seafood. But even the amount of seafood has declined, with only dried squid and "mingtai" fish still plentiful. "The North Korean fishermen don't have the gasoline to run the boats. Also their boats are quite old and [so is] their equipment," said Mr Huang.
North Korea's financial collapse began in 1991 with the break-up of its former economic patron, the Soviet Union. The floods of the past two years have wiped out much of the harvest and left hundreds of thousands of people homeless. Since then, an international aid effort has done its best to stave off mass starvation, but international sympathy has proved limited, not least because no one can be sure the food aid is not diverted to the army.
Nor can anyone know for certain the seriousness of the situation. Arthur Holcombe, the resident representative of the United Nations Development Programme (UNDP) in Peking believes there is widespread malnutrition in North Korea, with people rationed to just 700 calories a day. Children are suffering from night blindness, scurvy and rickets. So far, says the UNDP, people are not dying in great numbers, but Mr Holcombe warns that between June and September this year "there will essentially be no cereal grain crop available" and forecasts "a period of particular hardship".
Peering into North Korea from Tumen offers few clues. Along the river, Chinese entrepreneurs have set up telescopes for rent to Chinese tourists and to visiting South Koreans who journey here to get a glimpse of a forbidden land. On the other side of the river one can see the North Korean town of Nanyang, its railway station decked with two giant portraits of the late Kim Il Sung, and festooned with the slogan "Long live our Great Leader". The drab apartment buildings have plastic and boards in many windows, and apart from some children playing there are few people on the streets.
For Chinese over a certain age, it is like looking back in time. Until China's economic reform started in 1979, Yanbian people were poorer than their North Korean neighbours. "Our skates and cosmetics all came from North Korea," remembered the government official. Now it is a destination which makes Chinese people feel lucky.