China's leading search engine, Baidu, is earning almost a quarter of sales in China's rapidly expanding online advertising market, according to local analysts.

Google ranks fourth with almost 10 per cent of the country's total online ad revenues, researchers from Analysys International estimate.

More than $214m was paid to place online ads in China during the second quarter. Total revenue generated from ad placements rose 19.2 per cent compared to the first quarter, and was up 31.3 per cent compared to a year ago.

Baidu, which has taken many cues from Google's success in the West in establishing a Chinese search and ad network, retained its position as ad sales leader with 23.5 per cent of the market.

Two local portals, Sina and Sohu, held 18.8 per cent and 13.3 per cent respectively, according to Analysys.

Google took 9.2 per cent of the market in the quarter, while Yahoo's joint venture with China's Alibaba took 6.4 per cent.

Driven by strong advertising sales and sponsored search results, Baidu's second-quarter revenues were well ahead of predictions at almost $53m.

Company sources forecast revenue to exceed $64m in the third quarter, an increase of approximately 20 per cent.

Analysys did not explain the source of its ad sales data in its announcement of the results.

However, the major local players are listed on the US Nasdaq market and typically publish details of their revenue from key sectors, including advertising sales in some cases.