China's state-owned oil company, CNOOC, announced the opening of bidding for 33 reserve areas off the Chinese coast, including South China Sea areas.

China National Offshore Oil Corp. put 33 blocks totaling 48,691 square miles on the auction block. Seven of the 17 blocks for sale in the eastern basin of the Pearl River are in deep waters, with the rest scattered throughout the South China Sea.

CNOOC is trying to reverse sagging production from mature fields. During the first half of the year, production from the Bohai Bay, which accounts for more than half of all Chinese production, declined 2.5 percent from last year to 411,000 barrels of oil equivalent per day.

Five of the areas up for auction are on frontier territory.

China is suspected of making a land grab with some of its actions in disputed maritime territory.

CNOOC early this year deployed drilling rig HD-981 to an area about 120 miles off the coast of Vietnam.

The Vietnamese government said it would take "all the proper and necessary measures" to protect its interests, saying the rig was encroaching on its sovereignty.

CNOOC in August scored a success with a gas discovery offshore last month. Twelve of the blocks up for bidding were offered during a 2013 auction.