"The index generally sees the annual lows in April but the unique circumstances resulting from COVID-19 have meant that April was instead the first signs of recovery," Marex Spectron's global head of analytics Dr Guy Wolf said.

The index put the April average at 87.2, up from 86.7 in March and compared with 85 a year ago and 84.8 in April 2018. 

Activity was weakest at the start of April with the Easter period seemingly used for maintenance in most regions, the statement said.

"Indications from the product data in May are that the pick-up in activity has accelerated, particularly in China," Wolf said.

The index uses satellite data to monitor up to 90% of global copper smelting capacity.

Earth-i said two more Chinese copper smelters, Chifeng and Qiqihar, were added to the index earlier this month which took SAVANT's smelter coverage up to 82% of the Chinese market.

CRU last week said the effects of the COVID-19 pandemic were expected to be long-lasting and the consultancy now expected copper demand to fall 5% for China in 2020, and 6% for the rest of the world, with the possibility looming of unsustainable surpluses over the next five years.