The pound rose against the dollar and government borrowing costs dipped as investors reacted to Prime Minister Liz Truss's resignation.
One analyst says the reaction suggested investors were "relieved" by the news, despite a lot of uncertainty remaining.
Business groups said the new prime minister would have to act quickly to restore confidence.
Government borrowing costs rose sharply last month after the government promised huge tax cuts in its mini-budget without saying how it would pay for them.
Mr. Hunt is due to announce plans for spending and tax on 31 October in his economic plan, which the Treasury confirmed was set to go ahead.