Karachi: Pakistan stocks tumbled, driving the benchmark index to a six-month low, after a lawmaker proposed extending a new tax on gains from equities.

The Karachi Stock Exchange 100 Index fell 2.55 per cent to 9,229.6 at 4.50pm, headed for the lowest since December 21, after former finance minister and opposition lawmaker Ishaq Dar suggested a new capital gains tax on shares be applied retrospectively.

Only seven shares rose on the gauge, while six were unchanged and 87 slid.

"The comment created panic among investors," said Arif Habib, chairman of Arif Habib Group, which includes a brokerage.

Finance Minister Abdul Hafeez Shaikh announced in his annual budget speech that a capital gains tax would be imposed for the first time since 1976, on shares bought after July 1.