Mumbai: The Bombay Stock Exchange (BSE) benchmark Sensex plummeted nearly 120 points in opening trade on Monday on fresh selling by funds and retail investors amid a weak trend on other Asian bourses and hike in petrol prices by state-run oil companies.

Sensex, which had gained 195.49 points in the previous session, suddenly fell by 119.88 points to 18,411.40 within the first few minutes of trade, with auto, banking, metals and realty sector stocks coming under pressure.

The wide-based National Stock Exchange Nifty index also declined by 35.15 points to 5,509.60 points.

Brokers attributed the downward trend on the bourses to a fresh round of selling by funds and retail investors in tandem with a weakening trend on other Asian bourses and the biggest-ever hike in petrol prices of Rs 5 a litre by state-run oil companies.

Bucking the trend, state-run oil companies such as Bharat Petroleum, Hindustan Petroleum and Indian Oil Corporation were trading in the positive zone, as the hike in petrol prices will reduce their subsidy burden.

In other markets in Asia, Hong Kong's Hang Seng index was trading lower by 0.68 percent, while Japan's Nikkei shed 0.80 percent in morning trade on Monday.