China will gradually expand the sample size for measuring the Purchasing Managers' Index (PMI) from the current 820 companies to around 3,000 companies, authorities announced Tuesday.

The survey center under the National Bureau of Statistics (NBS) and China Federation of Logistics and Purchasing (CFLP) jointly made the announcement at a news briefing, saying they will produce more detailed PMI data as soon as possible.

The new PMI readings will vary from industries and regions, said the NBS and CFLP.

Sheng Laiyun, the NBS spokesman, said the PMI readout has played a unique role in predicting the economic trend in China in the context of global economic complexities, but with the landscape changing constantly, the survey needs improvements.

Sheng's view were echoed by Meng Qingxin, head of the survey center of NBS. He said with the economy developing, people have called for more precise and more detailed data.

The two departments did not give a specific timetable for the changes.

China began to publish the PMI in 2005. Currently the data is based on a survey of purchasing managers in 820 companies in 20 industries.