China on Friday denied abusing workers in Zambian copper mines, after a Human Rights Watch report accused Chinese firms of flouting health and safety laws while demanding up to 18 hours of labour a day.

"Regrettably, the relevant contents of the report is not faithful to the truth," the Chinese embassy in Lusaka said in a statement.

Four Chinese-run copper mines in Zambia are units of the state-owned China Non-Ferrous Metals Mining Corporation, under the authority of China's highest executive body.

Zambia, Africa's biggest copper producer, has welcomed Chinese investment but workers have often complained of sub-standard labour conditions.

In the report, workers described poor ventilation in the shafts, which can cause lung disease, failure to replace damaged equipment, and threats to fire miners who refuse to work in dangerous places.

Many miners at Sino Metals are required to work 12-hour shifts, five days a week, with a sixth 18-hour shift -- despite Zambian laws requiring a 48-hour work week, the report said.

The embassy said Chinese investors came to Zambia to create jobs for locals and to help develop the poor southern African nation.

"China has for a long time been investing in Zambia on the basis of mutual benefits, creating a large amount of job opportunities, and making great contributions to Zambia's social and economical development," the statement said.

"The Chinese companies concerned have always been closely following the local laws and regulations, actively undertaking their social responsibilities."

"They attach great importance to employees' legal rights, like safety, salary, and etc, and have taken serious measures to ensure the protection of those rights," read the statement.

Zambia's new President Michael Sata has vowed to clean up the mining industry and to improve the lives of the poor.

Resource-hungry China has invested an estimated $6.1 billion (4.3 billion euros) in the southern African nation since 2007, equivalent to more than one third of gross domestic product last year.