WRAPUP 3-Olympics-China's Games party set for "big bang" start

* Beijing to stage most expensive opening ceremony

* Bush flies into China after criticising rights record

* Pirate broadcast calls for political prisoners release

* Basketball player Yao Ming to carry China's flag

* Ronaldinho's Brazil, Messi's Argentina win in soccer

By Simon Denyer

BEIJING, Aug 8 (Reuters) - China celebrates its ancient past and modern power when the Olympics open on Friday, looking to put criticism behind it as world leaders arrived in Beijing.

The opening ceremony is the culmination of seven years of hard work that reshaped the capital, and sets the seal on a sustained economic boom that has seen China emerge as a new superpower.

"It's a historic combination of a great country with a great sport event," the People's Daily said.

Guests in the head-turning "Bird's Nest" Olympic stadium will include U.S. President George W. Bush, who flew in straight after making some of his bluntest criticism on human rights.

Displaying its new economic clout, China has invested $43 billion on the Games. Some $100 million, twice the 2004 Athens bill, has gone on "big bang" opening and closing ceremonies.

The elements, though, have proved stubbornly hard to master.

Authorities have closed factories and pulled millions of cars off the road, but smog and haze enveloped the capital on Friday morning -- obscuring views of the futuristic skyline.

It all kicks off at 8 p.m. on the eighth day of the eighth month -- the number symbolises fortune here -- before an estimated global audience of one billion.

With 12 hours to go, foreign activists issued an on-air challenge to the host city with a pirate broadcast, calling for freeing of political prisoners and lifting of censorship.

Paris-based Reporters Without Borders said China's attempts to control the media "would never succeed". Their words were often drowned out by a local official broadcast.