Mumbai: The BSE benchmark Sensex rose by nearly 89 points in opening trade on Wednesday, extending its gains for the fourth straight session on continued buying by funds and retail investors, tracking a firm trend on other Asian bourses.

The 30-share BSE index, which has gained nearly 105 points over the past three sessions, rose  further by 88.81 points, or 0.50 percent, to 17,658.34 in the first five minutes of trade on Wednesday, with stocks of metal, oil and gas, auto, realty and consumer durable companies leading the rally.

In a similar fashion, the wide-based National Stock Exchange Nifty Index moved up by 28.15 points, or 0.53 percent, to 5,317.50.

Stocks of state-run SBI witnessed keen demand ahead of its second quarter earnings announcement, gaining 1 percent to Rs 2,018.25 apiece in early trade on Wednesday.

Brokers said the trading sentiment in the domestic market was buoyed by a firming trend on other Asian bourses following overnight gains in the US after Italian Prime Minister Silvio Berlusconi said he would resign, raising hopes the debt-ridden country would proceed with reforms to contain the euro zone's sovereign debt crisis from spreading.

In the Asian region, Hong Kong's Hang Seng Index rose by 1.68 per cent and Japan's Nikkei Index by 0.68 percent in morning trade on Wednesday. The US Dow Jones Industrial Average closed 0.84 percent higher in Tuesday's trade.