March arrivals of copper concentrate, or partially processed copper ore, were at 1.77 million tonnes, according to the General Administration of Customs data. That is up 10.6 percent from the same month last year.
The shipments were down compared to February's 1.93 million tonnes, which tied the record hit in September 2018 despite having only 28 days and including the week-long Lunar New Year holiday.
"I think in February the import number was too strong, and that's why they didn't import so much in March as they were restocking ahead of Chinese new year," said Helen Lau, metals and mining analyst at Argonaut Securities.
China also imported 391,000 tonnes of unwrought copper last month, customs said, up 25.7 percent from 311,000 tonnes in February but down 10.9 percent from March 2018.
Unwrought copper includes anode, refined and semi-finished copper products.
Expanding smelter capacity in China has led to greater competition for copper concentrate. As a result, the treatment and refining charges (TC/RCs) that are paid to process concentrate into refined metal have fallen sharply.
Unwrought copper imports have been supported by demand from scrap consumers seeking other forms of the metal after China cracked down on scrap copper imports as part of a campaign to clean up the environment.
China's aluminium exports, meanwhile, rebounded from a two-year low in February and hit its second highest on record, Chinese customs data showed.
The March aluminium exports were 546,000 tonnes, up 59 percent from 343,000 tonnes in February and up nearly 21 percent from 452,000 tonnes in March 2018.
"The aluminium prices are lower since the value-added tax reduction. China has produced a lot of aluminium and there is an incentive to export," Lau said.
Besides the February blip, Chinese aluminium exports have been riding high since semi-finished aluminium products were given a higher value-added tax (VAT) rebate from November.
China reduced the VAT on the manufacturing sector to 13 percent from 16 percent starting on April 1 to ease pressure on its economy.
(Reporting by Shivani Singh and Tom Daly; Editing by Joseph Radford and Tom Hogue)