One of Margaret Thatcher's mining union foes has described the former PM's death as the icing on the cake as he celebrates his 70th birthday.

Belgium's justice minister ordered an inquiry Wednesday linked to a growing controversy over possible tax fraud among diamond traders in the port city of Antwerp.

Australian stocks had plunged by more than four per cent at noon, following falls of over five per cent on Wall Street overnight, as carnage on overseas markets spread to the local bourse amid fears the world could tailspin into a new recession.