BEIJING — Sales by China's biggest excavator manufacturers almost doubled in 2017, the latest sign of recovering economic activity.

Twenty-five leading digging machine makers sold more than 140,000 excavators last year, surging 99.5 percent year on year, according to the latest data from an association tracking the industry's development.

Domestic sales grew by 107.5 percent year-on-year to reach over 130,000 digging machines, while exports rose 32 percent compared with 2016 to sell over 9,600 digging machines overseas.

Chinese leading machinery maker Sany Heavy Industry Co Ltd sold over 30,000 digging machines last year, reporting both booming production and sales across the entire range of products.

In December, the 25 excavator makers sold over 14,000 digging machines, up 102.6 percent year on year.

Sales of digging machines are a telling indicator of the vitality of a country's economic activity as growing demand for them is usually backed by booming mining and infrastructure development.

Given the prospects for stable economic expansion and a high comparison base, analysts estimated that digging machine sales in China might grow 10 percent to 20 percent in 2018.