China's main stock index climbed 1.11 percent on Thursday, recapturing the psychologically key 4,000 level after a tumble two days ago, but some traders said fears were rising of a bubble in the market.

The Shanghai Composite Index ended the morning at 4,030.135 points, after closing below 4,000 the previous two days.

Gainers outnumbered losers by 759 to 108. Turnover in Shanghai A shares was very heavy at 95.4 billion yuan, up from Wednesday morning's 90.3 billion.

"I cannot deny there exists a bubble, and authorities have noticed that already," said Li Shiming, analyst at Galaxy Securities. "But warnings have been issued by regulators to cool the market."

Li said regulatory measures had not been severe enough, however, to rattle retail investors, and he expected the index to keep rising in the near term.

He added that blue-chip shares, especially in the banking sector which led the market lower during Tuesday's sell-off, had stablised, lending support to the market.

Chinese Premier Wen Jiabao said on Wednesday that China faced problems of excess liquidity and its foreign exchange reserves were too high.

Recent economic data, including Thursday's announcement of a 25.5 percent rise in urban fixed-asset investment during the first four months of the year, also reinforced expectations of further policy tightening to cool the country's economy and markets.

The communications sector benefited from the announcement on Wednesday that China had completed testing of globally accepted third-generation wireless phone standards, known as WCDMA and CDMA-2000, and they will be deployed in the mainland along with a home-grown standard.

Zhenhua Tech surged 6.91 percent to 12.37 yuan and China Unicom rose 2.44 percent to 6.31 yuan.

In the raw materials sector, Yunnan Copper climbed 3.30 percent to 24.40 yuan while Tongdu Copper was up 4.47 percent to 16.36 yuan, defying a drop in copper prices to their lowest in six weeks as strong Chinese import figures fuelled worries about excess supplies.

Zhang Xiaoqiang, deputy head of the National Development and Reform Commission, said China would encourage companies to invest in overseas resource firms to help break a bottleneck in the country's rapid economic growth, China Business News reported.

CITIC Securities jumped 5.15 percent to 59.78 yuan after it injected fresh funds into its Hong Kong unit, which would enhance its competitiveness in Hong Kong. ($1 = 7.68 yuan)