BP shuts down part of leak as black tide hits islands

The first oil from the BP spill in the Gulf of Mexico was reaching solid land yesterday, heralding the next phase in a disaster that has been unfolding in slow-motion for two weeks.

From a height of just 200ft, the leading edge of the vast and still-expanding slick could be seen beginning its deadly embrace of the Breton National Wildlife refuge, a tiny island off the coast of Louisiana that is one of the region's most important nesting grounds.

The news came as BP reported some cause for hope in its efforts to staunch the leaks feeding the slick. A shut-off valve has now been attached by robot submersibles to the end of the broken drill pipe, stopping the least significant of the three main leaks. And a first coffer dam – a four-storey steel box – began its journey to the spill site last night.

The coming days will be critical in determining the future course of the crisis. Calm winds allowed for widespread spreading of dispersant chemicals yesterday on the slick. BP engineers continued releasing chemicals close to the leak in an effort to reduce the quantities rising to the surface. Officials said that controlled burns in some of the thickest parts of the slick were also due to resume later yesterday.

As political leaders in Washington prepared a series of hearings into the 20 April accident, the Senate majority leader, Harry Reid, threw his weight behind plans to raise the liability cap on companies responsible for oil spills from $75m to $10bn.

At the Breton Reserve some of the booms laid appeared to have broken loose and were lying across the beach instead of in the water. There was no evidence of any personnel on the island to repair the defence.

There were separate reports last night of the oil also reaching the Chandeleur Islands, another, much larger, offshore chain.

The closing off of the end of the drill pipe has not reduced the quantities of the oil entering the ocean, but it was nonetheless heralded as an important step forward by BP. It "does enable to us to make progress, to winnow down the focus from three leaks to two," said spokesman John Curry.

The valve was successfully attached to the pipe late on Tuesday evening. The operation only became possible when seas calmed after a weekend of storms. The submersibles are directed remotely from operators in ships above.

It also emerged last night that in private, closed-door testimony in Congress, a BP executive had conceded that unless it is brought under control the ruptured well could leak as much as 60,000 barrels a day – more than ten times the volume estimated at the moment.