WASHINGTON - The U.S. Pavilion in 2010 Shanghai World Expo passed 400,000 visitors on May 13, and is projected to pass the half million mark by Sunday, U.S. Ambassador to China Jon Huntsman said on Friday.

Huntsman made the remarks in a press briefing on Secretary of State Hillary Clinton's upcoming visit to the Shanghai Expo, adding that the U.S. Pavilion is on track for one million visitors per month as predicted.

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Clinton will visit China later this month and visit the Shanghai Expo and the U.S. Pavilion, whose theme "speaks to the best of America."

"It speaks to innovation, sustainability, diversity, creativity, it projects great enthusiasm, and I know the secretary is going to enjoy it enormously," said Huntsman.

He highly appreciated what the Chinese government has done in hosting this event.

"I want to thank the Chinese government and the city of Shanghai for their very very hard work in organizing the 192 countries and countless organizations that are part of the Expo," he said. "It has allowed us to participate in a meaningful and significant way in public and commercial diplomacy, in ways that would otherwise be absolutely impossible."

"I guess the only way to properly to describe it is it would likely be the biggest event that ever was, with 70 million people funnelling through the various national pavilions during that time," the ambassador added.

The Shanghai Expo officially opened on May 1 and runs through October 31, 2010. With an estimated 70 million visitors, it will be the largest Expo (or World's Fair) in history.