Three days after the Shanghai World Expo opened, the coastal city's sweltering?weather kept crowds down by about half.

On May 3rd, when daytime temperatures in Shanghai touched 30 degrees Celsius, Expo visits plummeted to about 130,000, almost half of the first two days' average. About half a million tourists with fixed-day tickets simply didn't turn up at all, according to the Yangtze Daily.

The unexpected slump gave visitors to the congested Expo a bit of relief, where long lines are ubiquitous, easing pressure on public security and service maintenance, said Hong Hao, chief of the Expo Coordination Bureau.