More global copper smelters were not operating in March than in the first two months, data from satellite surveillance of metal processing plants showed, after Chinese smelters proposed to cut output and operations elsewhere undertook planned maintenance.

Earth-i, which specialises in observational data, tracks smelters representing up to 90% of global production for its SAVANT service and sells data to fund managers, traders and miners.

The company said that an average of 17.7% of global copper smelter capacity monitored was inactive in March compared with 11.5% during January and February combined.

Average inactive capacity in China rose to 9% in March from 8.3% in the first two months, it added in a statement on Thursday.

China's top copper smelters proposed in late March to cut production by 5% to 10%, sources told Reuters, after the world's top producer of refined copper battled short supply of raw material and losses at some operations.

"As market watchers seek confirmation of pledged curtailments in China ... inactivity in the country jumped sharply in the final days of March, ending the month at a substantially higher 12.8%," Earth-i said.

Outside China, the Isabel plant in the Philippines has shown "flickers" of inactivity, along with Codelco’s Chuquicamata smelter in Chile, it added.

"We are now entering a period of several scheduled maintenance closures."

(Reporting by Eric Onstad;Editing by Elaine Hardcastle)