A view of the World Horticultural Exposition in Nanhu Lake Park, in Tangshan, North China's Hebei province on Thursday. The World Horticultural Exposition begins on April 29, 2016. [Photo by Wu Yan/chinadaily.com.cn]

Tangshan, a key industrial city in North China's Hebei province, has been holding the World Horticultural Exposition since Friday, showing its determination to develop its economy in a green way.

Themed "City and Nature, Phoenix Nirvana", the expo includes six international and national flower competitions among other economic and trade, cultural and sports activities. The expo will last 171 days to Oct 16.

The core idea of the expo is to call for "a low carbon lifestyle and the harmonious coexistence between city and nature", said Xie Guilin, Director of Executive Committee Office and Deputy Secretary General of Tangshan government at a press conference on Thursday.

The site of expo, Nanhu Lake Park, was a coal mine. On July 28, 1976, Tangshan was struck by a magnitude 7.8 earthquake and the coal mine sank. The area that sank gradually filled with water and household waste.

In 1996, Tangshan started to rehabilitate the descended area and turned it into a park, eventually making it an attractive tourist spot, after a 20-year effort.

"Nanhu Lake Park will become a great example of an ecological restoration of a coal mine's descended area," said Xie.

As a cradle of China's modern industry, Tangshan leads the country in heavy and chemical industry, such as steel, coal, chemical and equipment manufacturing.

Though Tangshan's Gross Domestic Product (GDP) dipped to 610 billion yuan ($ 94 billion) from 622.5 billion yuan, it still ranks first in the Hebei province and at the top of the country's list.

"The site of the expo has become a green lung for the city," said Wang Chunyan, Deputy director of Tangshan city commission of urban planning, "it reveals how an energy consuming city turns into a low-carbon and environmentally friendly city."