At 12.30pm, the key index was down 20.01 points to 1,613.18.
Amid the volatile price action was fears that the country would come under another round of lockdown as the number of coronavirus cases continued to surge.
The country's industrial production index for November 2020 showed a contraction of 2.2% year-on-year, which was a disappointing result compared to Bloomberg's survey of economists' median forecast of 0.2% growth.
"With the prospects of the economic recovery clouded by the rising number of Covid-19 cases, we think that the lower liners may continue to remain under pressure over the near term on mounting concerns over the disruption of the supply chain with numerous factories and retail outlets temporarily closed," said Malacca Securities Research.
The research house is upbeat on the healthcare sector as it expects a resumption of buying activity on concern over the prolonged pandemic. Meanwhile, it also expects the rise in crude oil prices to provide further uplift to the energy sector.
Investors took profit off glove counters following Friday's rally. Hartalega dropped 38 sen to RM12.12 while Top Glove lost 13 sen to RM6.37 and Supermax slid 22 sen to RM7.08.
Bank stocks also declined, led by Maybank slipping 24 sen to RM8.16, Public Bank falling eight sen to RM20.26 and Hong Leong Bank dropping 10 sen to RM18.08.
Among the other heavyweights on the decline, Petronas Chemicals fell 27 sen to RM7.29 and Tenaga shed 18 sen to RM10.34.
Among the top actives, Bintai Kinden surged 11.5 sen to 70.5 sen on the back of 197.37 million shares traded on the back of its distributorship agreement for Greenie Medi cold chain boxes.
AT Systemization lost 0.5 sen ot 18.5 sen and DGB shed 5.5 sen to 19 sen.
Meanwhile, Japan's markets were closed today for a national holiday. In ther key Asian markets, China's Composite Index was down 0.2% while South Korea's Kospi dropped 1.6%.
Hong Kong's Hang Seng rose 0.9% while Australia's ASX200 slipped 0.8%.