By Michael Bristow
BBC News, Qinhuangdao
Throughout the night, workers at China's largest coal port are busy loading waiting ships with thousands of tons of "black gold".
Men and machinery at the port have been working desperately
These vessels mostly deliver their precious cargo to ports all along China's south-eastern coastline.
Qinhuangdao is now working overtime to supply southern areas that are experiencing their worst winter weather in more than 50 years.
There is a desperate need for coal at power stations that have had to limit electricity generation because a shortage of supplies.
The snow has revealed just how much China relies on its most abundant energy source.
In Qinhuangdao, port mangers and workers have one main task to complete - ship as much coal south as quickly as possible.
"We're not suffering like people down there so it doesn't matter if we have to work over Chinese New Year," said a port railway worker as he watched another coal train trundle passed his signal box.
Trains arrive at the port with dirty, dusty cargo
Chinese President Hu Jintao paid a flying visit to Qinhuangdao last week to tell the port authority to increase the amount of coal it handles.
"Your efforts are very important to ensure electricity to disaster-hit areas," he told enthusiastic dockside workers.
The port, in Hebei Province, has become an increasingly important transport hub since China began its economic reforms in the late 1970s.
It expanded three times in the 1980s and again in 2004. It mostly handles coal from the northern provinces of Shanxi, Shaanxi and Inner Mongolia.
The coal is dealt with quickly when it arrives.
Giant machines lift whole train wagons into the air before depositing the coal onto conveyor belts that take it to waiting ships.
Some of the coal is exported, but most is shipped to southern China, where the country's main manufacturing base is located.
It leaves behind its dirty legacy: across Qinhuangdao's port district thick coal dust clings to every surface.
Lin Song, of the port's publicity department, told the BBC that the port handled an average of 600,000-700,000 tons of coal a day in January.
That figure increased by 100,000 tons a day from 1 February after President Hu called for more shipments.
"Only by delivering this increased amount of coal can we satisfy the needs of power companies in southern China," she said.
The next few days are the most vital, according to Zhu Shangdong, head of the engineering department at just one of the port's coal handling companies.
"On Monday we worked day and night to ship 250,000 tons of coal. It gave me a very good feeling," he said from the end of a wharf that juts far out into the icy sea.
Ships take the much-needed coal south to power stations
Mr Zhu said men and machines were working at maximum efficiency.
The port had managed to cut the time it took to move coal from train to ship, added the man who shook the president's hand when he visited.
Despite the enthusiasm in Qinhuangdao, the current weather crisis has revealed flaws in the country's energy supply chain.
Writing in a national newspaper this week, Zhang Guobao, deputy head of the National Development and Reform Commission, said it should serve as a wake-up call.
He said the country is over-reliant on coal and needs to develop alternative energy sources, such as wind and nuclear power.
The core problem is that energy supplies are having trouble keeping up with the expanding economy, which grew by 11.4% last year.
Small mines closed
Even without this year's unusually cold weather, the authorities would have had difficulties meeting energy demands.
This situation has been exacerbated because the government has also closed many small and illegal coal mines that were deemed dangerous.
In what appears to be a change of heart, the government last week said some of these closed mines could reopen, but only if they were safe.
However much the government wants to develop other sources of energy, it admits it will have to rely on coal for a long time to come.
That is bad news for China, but good news for Qinhuangdao.