This aerial photo taken on April 27, 2023 shows the Lingdingyang bridge, which is part of the Shenzhen-Zhongshan link in south China's Guangdong Province. (Xinhua/Deng Hua)

A cross-sea highway project between the cities of Shenzhen and Zhongshan in south China's Guangdong Province is one step closer to completion.

The last pouring of concrete was put in place on Tuesday, as work on the immersed tube underwater tunnel, which spans around 6.8 km, is nearing its end, said Guangdong Provincial Communication Group Co., Ltd.

The tunnel is part of a 24-km-long highway connecting Shenzhen and Zhongshan, situated on either side of the Pearl River Estuary.

Shenzhen-Zhongshan link is a core transportation hub project in the Guangdong-Hong Kong-Macao Greater Bay Area. It consists of one underwater tunnel, two bridges and two artificial islands, making it one of the most challenging cross-sea cluster projects in the world.

The cross-sea link is scheduled to open to traffic in 2024. Once operational, the travel time between Shenzhen and Zhongshan will be reduced from the current two hours to approximately 20 minutes.

Shenzhen-Zhongshan link, along with existing structures like the Hong Kong-Zhuhai-Macao Bridge, will form a network of cross-sea and cross-river passages in the Greater Bay Area, boosting connectivity of the city cluster, said Deng Xiaohua, head of Guangdong Provincial Communication Group Co., Ltd.