Douglas Peake, the first mate of the supply boat that brought the box to the site, confirmed a radio transmission from the nearby vessel lowering the device that said the device would be in position over the well soon.

The transmission said undersea robots were placing buoys around the main oil leak to act as markers to help line up the 40-foot box.

The box was about 4,000 feet underwater before dawn Friday, with another 1,000 feet to go, Coast Guard Petty Officer Shawn Eggert said.

A crane late Thursday lowered the containment vessel designed to collect as much as 85 per cent of the oil spewing into the Gulf and funnel it up to a tanker. Eventually the crane would give way to underwater robots that will secure the contraption over the main leak at the bottom, a journey that would take hours. A steel pipe will be installed between the top of the box and tanker.