BEIJING - The net profits of Guotai Junan Securities, China's third-largest stock brokerage firm by assets, surged 348.2 percent in the first half of the year to 9.6 billion yuan ($1.6 billion), it said on Tuesday.

The company attributed the growth to a 544-percent jump in stock market transaction volume in the Shanghai and Shenzhen bourses during the period as well as its improved service, it said in a preliminary first-half financial report to the Shanghai Stock Exchange.

It said business income climbed 272.2 percent from one year earlier to 22.3 billion yuan during the January-June period.

Its shares gained 1.2 percent to 28.7 yuan on Tuesday.

On June 26, the company's shares soared 44 percent, the maximum allowed on a new stock's first trading day, in their Shanghai debut after the company raised more than 30 billion yuan, the largest domestic initial public offering in five years, despite a falling market.

Before China's market went into freefall on June 12, the key Shanghai stock index had risen by 152 percent since July 2014 and nearly 60 percent since the beginning of the year, with transactions constantly refreshing records.