SHANGHAI (AFP) - A pair of 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 1.5 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 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 men, 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.

A video of their feat, posted on YouTube on Wednesday, had received more than 1.5 million views and more than 9,500 comments by Thursday night.

Mr Raskalov said on his blog that they started the ascent on Jan 31, the first day of Chinese New Year.

"At that time the security was less watchful, workers were on vacation," 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."

The duo, who use the name "OnTheRoofs", could not be reached for comment. Media reports say they previously climbed the Great Pyramid of Giza.

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

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

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.