Once China’s capital, now one of the largest industrial cities in the world, Chongqing’s mountainous landscape and changing cityscape are like no others.

In 1938, with the Sino-Japanese war raging, Chongqing (then Chungking) was made the national capital by the Kuomintang, due to its strategic location. That same year, hundreds of bomb shelters were built into the sides of the mountains to provide protection against the onslaught the authorities knew would come.

Between February 1938 and August 1943, Chongqing was pounded relentlessly, the Japanese subjecting the city to a total of 268 air raids in which more than 11,500 bombs were dropped.

The attacks were designed to serve two purposes: to weaken Chinese defences and inflict civilian casualties to destroy morale.

The night of June 4, 1941, saw the heaviest death toll, when 2,500 people were injured or killed, the majority of those who lost their lives succumbing to suffoca­tion in the shelters. As many as 10,000 Chongqing residents died in total during the air raids.

The shelters that protected many who survived now have very different uses. Many have been converted into restaurants, shops and workshops. The 52 tunnels in the suburb of Fujiagou were put to use for industrial purposes, and until very recently were occupied by Jianshe, one of China’s most successful motorcycle companies. Machine parts were produced there.

The workers operated noisy machinery under flickering lights in stuffy conditions with poor ventilation – as they had done since the end of the war.

The Jianshe workers have now been relocated to another part of Chongqing as the government prepares to trans­form the Fujiagou tunnels into a museum and a memorial.

Elsewhere in the tunnel network, near the Liziba metro station, Ms Fang, the owner of a recycling business, is struggling due to a drop in the price of steel. Having moved from Sichuan province in 2000, she earned up to 2,000 yuan (HK$2,270) per tonne of steel until four years ago. Now she’s lucky if she gets 900-1,000 yuan per tonne.

Many of Chongqing’s wartime tunnels have been con­verted into workshops but demand for their services is falling. However, one advantage to operating a business in the tunnels are low costs.

The tunnel close to Lianglukou that married couple Ma Zhihua and Ning Pingzhi rent for their bicycle store and scooter workshop, for example, stays cool in the summer and warm in the winter, so they have no need for heating or air conditioning. Beyond the 3,000 yuan a month rent they pay, there are few overheads.

Roughly 2.5km of tunnels in the centre of the city are now part of the metro line between Linjiangmen and Jiaochangkou, with more under development in Lianglukou. The local government, meanwhile, has been transforming other surviving shelters for recreational uses.

Built to protect the population during time of war, and having helped the city become an industrial powerhouse, the tunnels of Chongqing are symbols of both suffering and regeneration.