Net long copper positions on US commodities exchange COMEX rose 15% to 85,485 contracts in the week ended July 25, the highest since February, Commodity Futures Trading Commission data showed Monday.
It was the second consecutive increase in bullish money mangers' positions, up 27% in the last two weeks, but below January's record net long position of just over 100,000 contracts.
Long positions are already at a record high of 121,087 contracts, against 35,602 short contracts.
Speculative investor support helped copper prices top two-year highs last week, three-month contracts on the London Metal Exchange moved above $6,400/mt Monday for the first time since May 2015.
Prices up 6% on the week and as much as 10% in the last two weeks have benefited from rising confidence in the Chinese economy as well as supply constraints.
Factory activity continued to rise in China in July, according to official data released Monday, although at a lower rate than June. Manufacturing PMI was reported at 51.4, versus 51.7 in June.
The world's second largest economy and biggest metals consumer recently reported economic growth of 6.9 % for the second quarter of 2017, above expectations and setting it on course for its first annual year-on-year growth rate since 2010.
China also surprised markets at the end of last week with an announcement to import less copper scrap from 2018. Expectations are for restrictions to apply to scrap with a low copper content of around 14%, which currently constitutes 60-70% of scrap imports into China, according to some analysts.
Warehoused copper stocks have fallen around 8% in the last three weeks, according to LME exchange data, to just below 300,000 mt Monday.
More generally, commodities have also been boosted by a weak dollar, falling to fresh multi-month lows against a number of major currencies in recent weeks, including its lowest in over a year against the euro.
Three-month LME copper was last bid at $6,365/mt at 1645 GMT Monday, up $40 from Friday's close but down from an intraday high of $6,430/mt.
