Heavy cloud and rain are likely to ruin the party for millions of people hoping to watch Wednesday's eclipse in Shanghai and other parts of eastern China, meteorologists said.
The Shanghai Meteorological Bureau bureau has predicted thunderstorms for when the longest solar eclipse of the 21st century starts at 8:30 am (0030 GMT), according to a forecast released on Tuesday morning.
"It will be almost impossible to see the eclipse in Shanghai," Li Jinyu, the bureau's chief service operator, was quoted as telling the Shanghai Daily.
"Even if there is no rain, the heavy clouds will block the view," he said.
However people will still experience the sky changing from bright to dark, the report said.
Eastern China has been regarded as one of the best places in the world to view the total eclipse, which is expected to last about six minutes and reach its midpoint around 9:30 am.
The event is being described as a once-in-a-lifetime opportunity which, due to its trajectory over China and India, could end up being the most watched eclipse in history.
A solar eclipse occurs when the moon is caught between the sun and the earth while each of them moves along their fixed orbits.
"This is a very important milestone. None of us will live long enough to see another one like it," said Federico Borgmeyer, the German-based manager of the specialist travel agency Eclipse City who is in Shanghai for the event.
The phenomenon has sparked a mini-tourism boom for Shanghai and other parts of eastern China, such as historic Hangzhou city.
Thousands of tourists from around the world have already descended on Shanghai, with hotels and restaurants in marquee locations such as the Bund being quickly booked out.
The next total solar eclipse will be on July 11, 2010 but far fewer people are likely to see it as it tracks across the South Pacific over French Polynesia and Easter Island to the southern tip of South America.