Financial authorities in New Zealand are investigating an incident of mystery trading this morning that causes an unexpected increase in the share prices of several major ASX200 shares.

The biggest gain was notices in the shares of ANZ, which rose from $25.96 to $27.63 at the opening of trade. The shares of the bank were trading at $26.08, up 0.5 per cent at the time of reporting this morning. Within a few minutes of trading huge volumes of shares exchanged hands.

The share prices of other companies including Ansell, Aristocrat and AGL were also affected. The shares of Commonwealth Bank and Bank of Queensland also recorded an increase when the ASX opened this morning due to mysterious trading activity.

A spokesperson for the Australian Securities Investment Commission, which is responsible for monitoring real-time trading, said that the agency was aware of the situation and is looking into the matter but pointed out that a formal investigation has not been launched.

ASX spokesman Matthew Gibbs said that the increase was due to huge demand order and was not relating to the trading system. He added, “There were a number of large buying orders at the market’s open, and the price of a number of stocks went up. Most of them appear to have come down now and are trading at a normal price band. Naturally ASX is monitoring the situation.”