Chinese shares slid more than 5 percent on Monday to a 20-month low, dragged down by heavyweights, as almost every issue lost ground amid the ongoing stock-market decline, the worst in a decade.

The benchmark Shanghai Composite Index tumbled 5.33 percent, or130.74 points, to 2,319.87. The Shenzhen Component Index closed at 7,833.09 points, down 400.32 points, or 4.86 percent.

Monday's losses further undermined the Shanghai index, which fell in the first four days last week, dipping from 2,605.72 points to 2,437 points, although it edged up 0.56 point on Friday.

Aggregate turnover on Monday rose to 52.39 billion yuan (7.62 billion U.S. dollars) from 47.19 billion yuan on Friday.

Losses outnumbered gains by 810-12 in Shanghai and 650-19 in Shenzhen.

Individual and institutional investors further lost confidence although the country's insurance regulator promised over the weekend to support the stock market. The regulator didn't elaborate, and the absence of details added to investors' fear, said analysts from www.cfi.net.

This week, there will be a large volume of shares coming out of lock-up periods for trading. A total of 18.9 billion non-tradable shares, which were valued at 120 billion yuan, would come onto the market this week.

Moreover, macroeconomic statistics released last week evidently showed an economic slowdown, another reason for the bearishness, said the website.

Coal shares slid, as China plans to raise the coke export tariff rate to 40 percent on Wednesday, from 25 percent.

China South Locomotive & Rolling Stock Corp. jumped as much as 58.26 percent on its first day of trading in Shanghai, a sign that demand for new shares is withstanding the steep declines in overall share values.

The nation's biggest maker of trains climbed as high as 4 yuan from an initial offer price of 2.18 yuan, before closing at 3.45 yuan.

Among the few sectors gaining was aviation. Market talk that state-owned China Aviation Industry Corp. I and Corp. II might merge to build large aircraft spurred aviation shares to buck the downward trend, said dealers.

Guizhou Guihang Automotive Components saw its shares gain 7.49 percent to close at 8.9 yuan, while another aviation enterprise --China Aerospace Science and Technology Corp. -- rose 3.33 percent to 8.37 yuan.