At 12.30pm, the FBM KLCI was down 1,510.67, erasing the modest gains made in the previous session.
"Although investors will be shifting their focus from daily Covid-19 infections to the positive vaccination rate locally, the local sentiment may still remain cautious following the negative performances in China and Hong Kong after Beijing announced additional measures for the technology, education and real estate sectors," said Malacca Securities Research.
Press Metal led the fall on the blue-chip index, sliding nine sen to RM4.81.
Top Glove was down five sen to RM3.95 while Hartalega rose one sen to RM7.31, with Kossan's recent 1H earnings result unable to shore up sentiment in the gloves sector.
Financial stocks were mostly in the red led by CIMB down four sen to RM4.49 and Hong Leong Bank sliding six sen to RM18.16. Maybank rose two sen to RM8.02 while Public Bank was unchanged at RM4.01.
On the broader market, the country's technology sector was seeing some pullback led by Genetec down 40 sen to RM20, MPI sliding 26 sen to RM41.64, KESM falling 16 sen to RM12.30 and Globetronic shedding 14 sen to RM2.13.
Top actives were XOX unchanged at four sen, AT Sytemization flat at 6.5 sen and Artroniq up 7.5 sen to 48 sen.
In Asian markets, while China's and Hong Kong's equities found some stability after two days of furious selling, the overall sentiment remained dour.
China's main index was down 0.6% and Hong Kong's Hang Seng slid 0.25%.
Japan's Nikkei shed 1.5% while South Korea's Kospi lost 0.4%.
In Australia, the ASX20 was down 0.7%.