Mainland A shares plummeted more than 8 per cent on near panic-selling yesterday - their biggest one-day decline this year - on fears the worsening flooding would stall economic development. As the flooding moved northwards to threaten the country's prime oil-producers in Heilongjiang, panic-stricken investors dumped shares from the opening bell, wiping out 8.42 per cent off the Shanghai A-Share Index. The index finished at 1,138.35 points yesterday - its lowest since last September - on turnover of 3.4 billion yuan (about HK$3.16 billion). The Shenzhen A-Share Index tumbled 8.32 per cent to an 11-month low of 344.29 points. Turnover was 3.2 billion yuan. Traders said the avalanche of poor interims announced by listed companies had compounded growing concern over the country's worst flooding since 1954, further damaging investor confidence in stock markets. Companies like Ningbo Zhongyuan and Jinzhou Petrochemical, which posted profit drops of 99.37 per cent and 88.57 per cent, respectively, were the main culprits for investors' mark-down of the overall corporate outlook. Both A shares fell to their 10 per cent daily price limit yesterday. 'Based on their interim reports announced so far, the prospect on the corporate level was not optimistic,' a Shenzhen-based broker said. Of more than 770 A shares listed in Shanghai and Shenzhen, only about a quarter of them have published their interims, most to analysts' dissatisfaction. Shenyin & Wanguo Securities analyst Zhang Lan said investors had started to feel the pinch of the severe flooding as it widened from the Yangtze River region in central China to the northeast, and to gauge its impact on listed companies and the affected regions. Official media have reported that floods along the Yangtze have led to more than 2,000 deaths and affected up to 240 million people. In the northeast, floodwaters have already inundated 1,217 oil wells in marsh land outside Daqing city, which accounts for half of the country's oil production, forcing the closure of 527 wells in the city. 'Central China plays a big part in the country's economic development, the flooding is expected to add more woes to Beijing's economic growth target,' the Shenzhen broker said. Beijing aims to achieve a projected 8 per cent economic growth target this year, but is under growing pressure to lower it because key growth engines - exports and foreign investments - had slowed. B shares were closed in Shenzhen yesterday. Hong Kong was closed for a public holiday. In Shanghai, the B-Share Index fell 1.56 per cent to 27.18 points.