The 30-scrip sensitive index (Sensex) of the Bombay Stock Exchange (BSE) built on early gains and was ruling 339 points up during noon trade on the back of optimistic signals from other Asian markets that surged after China declared that it will move towards a flexible currency.

The Sensex was ruling at 17,910.73, up 339.91 points (1.93%) from its previous close at 17,570.82.

At the National Stock Exchange (NSE), the broad-based Nifty was ruling 1.9% up at 5,362.65 from its previous close at 5,262.6.

The BSE midcap index was ruling 1.35% up and the BSE smallcap index surged 1.38%.

Metals, realty and banking scrips were among the major gainers and all the 13 sectoral indices on the BSE were trading in the positive terrain.

Asian bourses witnessed more broad-based buying after Chinese authorities announced that it would make the Yuan, which has been pegged to the US dollar, more flexible, bringing relief to foreign makers.

Metal scrips rose together with growing costs of such commodities around the world.

The Japanese Nikkei ended at 10,238.01, up 2.43%, while the South Korean Kospi closed at 1,739.68, up 1.62%.

Hong Kong's Hang Seng was trading 2.96% higher at 20,056.25, while the Chinese Shanghai composite index was up 2.9% up at 2,586.21. (With Inputs from Agencies)