Apparel manufacturers in South Africa and other African nations are celebrating after the United States agreed to double its duty free clothing quota.

Friday's unexpected - but overwhelming - decision by the House of Representatives is expected to be rubber-stamped by the Senate later this year.

Also approved, as part of a bill extending trade preferences for Andean nations, were corrections to the African Growth and Opportunity Act (AGOA) that could unlock substantial new investment in several southern African states.

Paul Ryberg, director of the African Coalition on Trade, which has been lobbying for the bill on behalf of regional exporters, said the breakthrough was made possible by leaders in both chambers agreeing to decouple the Andean-African initiatives from legislation granting US President George Bush's "trade promotion authority" to negotiate trade treaties without congressional micromanagement.

The AGOA capped the amount of apparel African countries could ship to the US duty free to 1.5 per cent of overall US imports by volume, rising in small increments to 3.5 per cent in the year starting October 1, 2007.

Under the new changes, those limits will now be doubled, giving a welcome trade boost to qualifying African nations.