Fears are growing for four Americans whose yacht was captured a by pirates in the Indian Ocean off the Somali coast.

A rush-hour crawl that gave vehicles little momentum to slide into the river and a bridge design that minimised falling debris appear to have kept the death toll relatively low in the collapse of a bridge into the Mississippi River.

Families waited anxiously for news of missing relatives as divers searched through the dangerous debris left by Wednesday’s bridge collapse.

An Islamic militia with alleged al-Qaida links has seized Somalia’s capital Mogadishu after weeks of bloody fighting with US-backed secular warlords, raising fears that the nation could fall under the sway of Osama bin Laden’s terrorist organisation.