SHANGHAI, July 7 (Reuters) - China's main stock indexes slumped over 5 percent at one point on Tuesday but ended the session down less than 2 percent, aided by intensified buying of index heavyweights listed in Shanghai, though small caps in Shenzhen continued to slide.
Top lenders Bank of China and China Construction Bank surged their upward limit of 10 percent. So did the shares of oil giant PetroChina, major insurer Ping An and China Railway Construction.
As a result, the SSE 50 index, which tracks the biggest 50 listed companies in Shanghai ended the day up 2.3 percent.
But the benchmark stock indexes still fell, wiping out Monday's gains, despite a slew of emergency rescue measures announced over the weekend.
The CSI300 index of the largest listed companies in Shanghai and Shenzhen fell 1.8 percent, to 3,928.00, while the Shanghai Composite Index lost 1.3 percent, to 3,727.12 points.
Shenzhen's growth board ChiNext slumped 5.1 percent.
In Shanghai, only 58 stocks rose while 812 companies fell. In Shenzhen, 25 companies gained and 1,209 declined.
The afternoon surge in China's biggest companies came amid reports that 21 Chinese brokerages had shifted over 128 billion yuan ($20.62 billion) into a stabilization fund to buy blue chip exchange-traded funds.
In addition, 57 mutual fund houses said they have started buying equity funds using a combined 2.16 billion yuan of their own capital, with a focus on blue chips. (Reporting by Samuel Shen and Pete Sweeney; Editing by Richard Borsuk)