BEIJING, July 2 (Xinhua) -- China's major Internet firms reported double-digit growth in combined revenue in the first five months, official data showed.

Companies above the designated size in Internet and related sectors raked in 428.2 billion yuan (62.5 billion U.S. dollars) from January to May, up 19.4 percent year on year, according to the Ministry of Industry and Information Technology (MIIT).

The pace picked up 2 percentage points from the first quarter, MIIT said.

R&D investment in the sector maintained fast expansion by rising 15.6 percent year on year to 18.12 billion yuan in the period.

Revenues of information services, making up 69.5 percent of the Internet business revenue as the biggest contributor, surged 21 percent to 297.8 billion yuan during the period, while that of Internet data services recorded the fastest growth of 36.5 percent to 4.13 billion yuan.

Guangdong, Shanghai and Beijing saw their Internet business revenues up 12.2 percent, 25.3 percent and 19.5 percent respectively year on year in the first five months.