Namibia's mining sector is centred around uranium, with the Rossing and Husab mines accounting for more than 10% of global supply.
China-backed Rossing Uranium, previously controlled by Rio Tinto, said it would stop normal operations on Saturday "and enter a period of minimal mining operations", with critical maintenance work to continue.
Other assets of significance include B2Gold's Otjikoto mine, which produced 177,966 ounces of gold in 2019.
Namibia declared a state of emergency on March 17 and implemented a 30-day worldwide travel ban. Most people are now working from home. The country has yet to record any COVID-19-related deaths.
Namibia's measures follow the same timeline as those of its southern neighbour South Africa, which shut down its mining sector for three weeks as of midnight on March 26.