SHANGHAI, Nov. 16 (Xinhua) -- Four countries from Europe and Asia signed participation contracts with the 2010 Shanghai World Expo on Friday as organizers unveiled the themes of their national exhibition pavilions.

Nepal, the Netherlands, Poland and the United Arab Emirates (UAE) inked legal contracts with the expo, bringing the number to nine countries who have officially signed. Switzerland, Britain, Hungary, Luxemburg and Spain had previously signed.

"With the signing of more and more countries, the organization work of Shanghai World Expo has entered a new phase of fulfilling legal procedures from political promises of the international community," said Hong Hao, a chief coordination official with the expo.

So far, 180 countries and international organizations have confirmed their participation. Organizers aim to attract more than200 participants in total to make the event the biggest on record.

The Netherlands plan to invest 20 million euros (about 29.4 million U.S. dollars) in its pavilion named "Happy Street." It will consist of 17 separate tiny houses to demonstrate the country's innovations in utilizing space, energy and water resources.

The 6,000-square-meter UAE pavilion is one of the largest pavilions at the expo. It will showcase energy use, protection of traditional culture and ideas for future cities.

Nepal's pavilion, under the theme of "Tales of Katmandu", will exhibit the history of the art and architecture in its capital, and the country's efforts in environmental protection, renewable energy and energy-saving buildings.