China is preparing an arsenal of rockets and aircraft to protect the Olympics opening ceremony from rain, hoping to disperse clouds before they can drench dignitaries at the roofless "bird's nest" stadium.

Officials believe there is a 47% probability of rain during the August 8 opening ceremony and a 6% chance of a heavy downpour and will try to drain humidity from clouds before they reach Beijing.

More than 100 staff at 21 stations surrounding the city will have 10 minutes' notice to fire rockets or cannons containing silver iodide at approaching clouds in the hope of making them rain before they reach the stadium. Three aircraft will also be on stand-by to drop catalysts to unleash rain from the clouds.

"We've worked with neighbouring provinces on a contingency plan for rainstorm and other weather risks during the ceremonies," said Wang Yubin, the deputy chief of China's meteorological service assigned to the Olympics.

The government has spent $US500,000 to build up Beijing's cloud seeding capacities over the last five years and authorities will conduct practice runs in June and July. It typically uses pellets of silver iodide, which is highly insoluble in water and can concentrate moisture to cause rain.

Zhang Qiang, head of Beijing's Weather Modification Office, believed her staff can fend off drizzle, but could be powerless in the face of a heavy downpour.

"I hope God will not send any storms to Beijing," she said.