A pair of Russian daredevil climbers ascended to the top of the world's second tallest building in China's commercial hub Shanghai, posting a stomach-turning video which has received more than a million views.

The duo, who identified themselves as Vadim Makhorov and Vitaliy Raskalov, said they scaled the Shanghai Tower, which will reach over 630 metres (2,067 feet) when it is finished this year if construction goes according to schedule.

Globally it will be second only to the Burj Khalifa in Dubai, which stands at 828 metres.

The video showed the two, wearing black hoodies, walking up stairs, climbing ladders and finally scaling a crane at the top of the Shanghai Tower as they peered at buildings shrouded in clouds below.

Raskalov said on his blog that they started the ascent on January 31, the first day of China's Lunar New Year.

"At that time the security was less watchful, workers were on vacations," he said.

"It took us almost two hours to get on the 120th floor by foot. And also, we (spent) almost 18 hours on top of the building, sleeping and waiting for better weather."

A video of their feat, posted on YouTube (www.youtube.com/watch?v=gLDYtH1RH-U) had been viewed nearly 1.8 million times on YouTube and more than 1.4 million times on Chinese site Youku.com.

Raskalov said he "surprised" by the number of views in a short email interview with AFP.

Commenting on his illegal ascent of Shanghai Tower, he admitted: "It was very risky if the police or security guards had caught us, we would have been deported and banned for a period ranging from five to 20 years."

The duo use the name "OnTheRoofs" and media reports say they previously climbed the Great Pyramid of Giza.

In China, where YouTube is blocked by authorities, the clip was re-posted to several video websites.

Many Chinese netizens were impressed by their antics, though some did highlight it was a violation of the law.

"My knees are getting weak just by watching. Hollywood blockbusters are nothing compared to this," said one poster.

The building's management said steps would be taken to bar any repeat performances, according to a statement carried by state media.

"Shanghai Tower will implement measures such as putting up wire fencing around the walls and installing safety doors on exits to avoid similar incidents from happening again," said the statement, which was carried by state television.