Members of South Africa's National Union of Mineworkers (NUM) are on strike over pay, regional secretary Cornelius Manhe said, after more than 600 members downed tools on Monday.

The London-listed miner had warned on Monday that there could be labour unrest as it finalises a new wage agreement for its operations in South Africa, sending its shares down 7 percent on the day.

It also said on Monday that it had resumed operations at its Williamson mine in Tanzania after a four-day stoppage, adding that its full-year production target remains unchanged.

Petra Diamonds had halted operations at the mine last week after the Tanzanian government seized a consignment of diamonds and questioned Petra personnel as part of a crackdown on the mining sector.

(Reporting by Justin George Varghese in Bengaluru and Zandi Shabalala in London, editing by Louise Heavens)