AMP has had a troubled year

Australia's corporate watchdog is investigating "unusual" share trades before insurer AMP's announcement that it was demerging its British and Australian operations.

The troubled company's shares fell 36% on Monday when they resumed trade after being suspended last Wednesday ahead of the surprise announcement.

Suspicions of insider trading were raised after a large number of futures shares were sold on Wednesday before the suspension, indicating institutional investors had been tipped off.

The Australian Securities and Investments Commission (ASIC) said it was looking into the two occurrences.

No evidence

"ASIC's inquiries centre on the circumstances surrounding unusual trading ... ahead of AMP Limited's announcement of its demerger plan," ASIC chairman David Knott said in a statement.

ASIC said there was no evidence to suggest AMP had acted improperly.

Australia's index of futures contracts fell an unprecedented 1% in 10 minutes late last Wednesday.

AMP shares gained five cents to A$5.65 on Tuesday.