The Chinese Academy of Sciences has asked police in eastern China to help find its missing weather balloon, thepaper.cn has reported.

Researchers from the CAS Institute of Atmospheric Physics lost the high-tech balloon at about 4:50 pm on Wednesday when it dropped to an altitude of 300 miles during metrological tests in Zhangqiu, Shandong province.

The missing whale-shaped balloon, which was filled with helium, is 2 meters long and 1 meter wide. It was unmanned and not carrying any confidential information, according to the institute's website.

Based on wind direction and speed, the balloon is believed to have landed in nearby Zibo, either in the Zhoucun or Zichuan district.

The institute has offered a 4,000 yuan ($600) reward for information on the whereabouts of the balloon and its instruments, as researchers want to retrieve the data collected for analysis.

So far, it has received only prank calls.

Cheng Si contributed to this story.