The foreign trade volume of the southern Chinese metropolis of Shenzhen increased 7 percent to 3 trillion yuan (about 442 billion U.S. dollars) in 2018, thanks to its booming private high-tech enterprises, said local authorities Thursday.

The annual imports and exports of the private sector grew by 12.9 percent, accounting for 53.8 percent of the city's total foreign trade volume and contributing more than 94 percent to its foreign trade growth, according to the Shenzhen Customs.

The high-tech firms have become Shenzhen's major driving force in its imports and exports and the city's expansion of its overseas markets. In 2018, 12 private companies in Shenzhen ranked among the top 100 foreign trade enterprises in China.

In 2018, Shenzhen's imports and exports to Hong Kong exceeded 680 billion yuan, an increase of 3.9 percent, accounting for 22.7 percent of the city's total imports and exports.

Its imports and exports to ASEAN countries and the Republic of Korea maintained double-digit growth.

Under the Belt and Road Initiative, the metropolis's imports and exports to countries along the routes also increased by 9.9 percent.

In terms of exports, mechanical and electrical products still dominated, occupying 78.6 percent of the city's total exports. High-tech exports took up more than half of the city's total exports.

As for imports, Shenzhen's high-tech imports including integrated circuits and liquid crystal display panels continued to rank first in the country.