MANILA - DMCI Holdings Inc. said on Monday its nickel mining units are laying off hundreds of workers and putting plans to ramp up production on hold, as a government crackdown has begun to take its toll on the beleaguered sector.

DMCI's Berong Nickel Corp will lay off over 300 seasonal workers in the coming weeks while its Zambales Diversified Metals Corp has already let go of more than 100 personnel, the conglomerate told the Philippine Stock Exchange.

Berong and Zambales Diversified are among the 10 mines, eight of them nickel ore producers, the government has suspended
as a five-week-old crackdown on mines accused of violating environmental rules continues.

The closures and the threat of more mines being suspended in the world's top nickel ore supplier lifted prices of the metal to a one-year high of $11,030 a ton on Wednesday.

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DMCI said its DMCI Mining Corp unit has suffered a 25 percent drop in nickel ore shipments in the first half of 2016 because of an earlier drop in nickel ore prices and is bracing for an even tougher second half because of the mine suspensions.

"Early this year, we were planning on expanding our operations. But with the suspension, we have no choice but to put everything on hold," DMCI Mining Corp President Cesar Simbulan Jr. said in a statement.

The DENR and the Department of Energy have also separately asked DMCI's coal mining unit, Semirara Mining Corp., to explain alleged environmental violations.