(Adds ASX investigation, new quote)
SYDNEY, Oct 18 (Reuters) - Australia’s stock market regulator and the exchange operator ASX said they would look into a spike in the price of some major stocks in the benchmark S&P/ASX 200 index at the start of trading on Thursday.
Stocks including Australia and New Zealand Banking Group (ANZ), gaming group Aristocrat Leisure, AGL Energy and pallets distributor Brambles jumped as much as 7 percent when the market opened at 10 a.m. local time (2300 GMT).
The Australian Securities and Investments Commission (ASIC) said in an emailed statement it had “commenced enquiries with the market participants involved in trading in these stocks and related derivatives.”
“This is not a formal investigation,” it added.
The ASX said it observed some “unusual trading” in the first “AB” group of stocks when markets opened and said it would examine what happened. The ASX opens trade in alphabetical order.
“Clearly what happened was not usual and ASX will closely examine to find an explanation,” ASX spokeswoman Matthew Gibbs said in a statement.
The ASX noted that Thursday was the expiry day for the October ASX 200 Index futures contracts, which often generates heightened activity as investors seek to unwind their positions.
The ASX said the affected stocks opened higher, but retreated to lower levels immediately after opening. It said trade throughout the rest of the day was orderly and the bourse was ready to assist the regulator if necessary.
Shares in ANZ soared 6.4 percent to A$27.63 at the open in heavy volume, before closing virtually flat. If sustained, the move would have been its biggest one-day climb since early 2009, during the global financial crisis. (Reporting by Jane Wardell; Editing by Sanjeev Miglani)