MORE than 10 people have died in China's commercial hub Shanghai, a local health official says, as the city grapples with its highest temperatures in at least 140 years.

Much of China is in the grip of a summer heatwave, and the China Meteorological Association issued a high temperature warning for several eastern and central provinces, saying temperatures could reach 41C on Wednesday.

Leng Guangming, a spokesman at the Shanghai Municipal Centre for Disease Control and Prevention, said there had been at least 10 victims of heat stroke up to last Friday in the city. He declined to give a more precise or more recent number.

City forecasters said temperatures were "rising rapidly" and could reach 40C in People's Square on Wednesday.

Experts blame a subtropical high pressure system and a lack of rain for the record-breaking heatwave, according to state media.

Pictures have shown people sheltering from the heat in air-conditioned shops or subways, and trying to cool off in swimming pools and rivers.

Footage of a slice of pork cooked through in 10 minutes on outdoor stone slab, taken by a Shanghai TV station, has gone viral online.

"It turns out that the only difference between me and roast meat is a pinch of cumin," joked one user of the Twitter-like microblog Sina Weibo.

Tuesday was the eighth consecutive day with temperatures above 38C in Shanghai, the official Xinhua news agency reported, citing the local weather bureau.

The temperature reached 40.6C last Friday, topping a previous high of 40.2C in 1934 and the highest since records began in 1873, Xinhua said earlier.