MELBOURNE, Oct 6 (Reuters) - Australia's competition watchdog...

MELBOURNE, Oct 6 (Reuters) - Australia's competition watchdog raised concerns about bids from the nation's two biggest coal haulers for Glencore Plc's coal rail business and said it would decide by December whether to allow them to go ahead.

Glencore has attracted several bids for its GRail business, the third-largest coal haulage business in Australia, which could fetch as much as A$1.5 billion ($1.1 billion), including from top coal hauler Aurizon Holdings (AZJ), its arch rival Pacific National and U.S. firm Genesee & Wyoming Inc .

The Australian Competition and Consumer Commission said the sale of GRail was a rare opportunity to introduce competition in the rail business.

"The Hunter Valley coal haulage market appears to have high barriers to entry, so we would expect the addition of a third competitor to have a significant effect upon the market," commission Chairman Rod Sims said in a statement.

($1 = 1.3141 Australian dollars)