LUSAKA - At least 10 subsistence miners were killed when a mine dump known locally as Black Mountain collapsed in Zambia's second-largest city and copperbelt mining hub Kitwe on Wednesday, police said.

The vast mound of dark earth in the country's northeast has become an economic lifeline for thousands of people who make a living from activities that local media report have been partially legalised. "So far we have retrieved 10 dead bodies and seven bodies of those injured," said Copperbelt Province police commissioner Charity Katanga.

Operations to retrieve bodies were ongoing, she added.

Local media reported that ministers were forced to step in last month after small-scale miners began using explosives to extract copper from the mine dump, damaging nearby properties and possibly dislodging the mound.

Zambia has some of the world's largest copper reserves and the metal accounts for as much as 80 percent of the country's export earnings.

High levels of unemployment have forced people to resort to illegal mining and in 2009 eight miners were killed in a similar incident.

"What we have are options on the table on how to deal with the Black Mountain. What is true also is that there is a lot of illegal mining taking place there which has to be stopped," former mining minister Christopher Yaluma told the Lusaka Times previously.

"We are also aware that young people need jobs to sustain their lives but, of course, generation of income needs to be done within the law."

After posting average annual growth rates of more than 10 percent in the 2000s, Zambian growth slowed significantly around 2011 due to falling copper prices.

A drop in copper prices of almost one-third from their peak in February 2011 resulted in thousands of job losses in the mining industry, where most companies are owned by foreign, notably Chinese, investors.

But Finance Minister Margaret Mwanakatwe has forecast growth will accelerate to four percent in 2018 as copper prices begin to recover.

The price of a kilo of copper has risen exponentially on international markets in recent years - mainly because of growing demand from China and India.

A pound of copper currently sells for $3.14 (2.74 euros), according to the InfoMine service.

That has made communications and power cables a valuable target, both for major gangs that steal large quantities from depots, as well as small-time thieves.