More than 10 people have died in China's commercial hub Shanghai, a local health official said Wednesday as the city swelters in its highest temperatures for at least 140 years.

Much of China is in the grip of a summer heatwave, and the China Meteorological Administration issued a high temperature warning for several eastern and central provinces, saying temperatures could reach 41 degrees Celsius (106 Fahrenheit) on Wednesday.

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

Temperatures surpassed 38 Celsius in almost all areas of Shanghai on Wednesday, peaking at 39.8 C in the central Xujiahui district in the afternoon, according to local weather statistics.

Authorities issued a "red" heatwave warning in the afternoon -- the highest level -- but later lowered it to "orange".

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

The heat was the top topic being discussed on the social networking site Sina Weibo, a Chinese equivalent of Twitter, on Wednesday afternoon.

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 Weibo user.

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

Tourists in lifebelts and bathing suits packed the "Dead Sea of China" resort in Sichuan, in the southwest, state media reported, adding the scene was ridiculed online as resembling "cooking a pot of dumplings".

Restaurants in Pianyan, in central China, moved hundreds of tables into the shallows of a river to let diners sit barefoot in the water.

In Loudi, in the central province of Hunan, a house had become a "natural incubator", China's national radio said, after a woman said she found chicken embryos in eggs that had been in a room for about two weeks.

Vehicles burst into flames in cities including Hangzhou and Taizhou, local papers reported.

Wednesday was the ninth consecutive day with temperatures above 38 C in Shanghai, according to meteorologists and reports.

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