With increased possibilities of heavy showers and a typhoon after days of sizzling heat, Expo 2010 Shanghai organizers have vowed to be well prepared for any type of extreme weather.

Shanghai received heavy rainfall on Tuesday, prompting the Shanghai Meteorological Bureau to lift the alert level from yellow to red.

Before the downpour, Shanghai witnessed 22 consecutive hot days, with the highest temperature reaching 40 C.

It was forecast that the hot days in Shanghai will continue for another week, with some days of extreme weather.

"It is common to see a sudden thunderstorm in Shanghai in August and September. In some areas, the precipitation will be extremely high," said Wu Rui, a weatherman from the Shanghai Meteorological Bureau.

With extreme weather looming over the city, Expo organizers are exuding great confidence in the venue's drainage system.

"The system is independent from other drainage facilities in the city. So the rainwater will be discharged into the Huangpu River to avoid water logging in the Expo Garden," said Xi Qunfeng, director of the project department of the Bureau of Shanghai World Expo Coordination.

Xi said the water sewerage standard applied in the construction process was higher than the average standard in Shanghai.

"The system was designed to fight off extremely heavy rainfall," said Xi.

Expo organizers are also prepared with large number of sand bags and equipment to respond in case the precipitation crosses the alert level.

Though there was no major water logging reported in the Expo Garden following the rain on Tuesday, some pavilions suffered minor leaks.

"We could see water dripping from the roof of the Japanese Industry Pavilion," said a visitor, surnamed Yong. "The leakage was not serious."

Some 420,000 people entered the Expo site by 7 pm on Tuesday.

Five on-site health clinics treated 414 visitors yesterday by 4 pm.

Xinhua contributed to this story