BP begins to funnel off leaking Gulf of Mexico oil
A new cap placed over a ruptured oil well in the Gulf of Mexico has begun to funnel oil to the surface.
US Coast Guard chief Adm Thad Allen said rough estimates showed that 1,000 barrels a day were being captured.
This is only a small part of the 12,000-19,000 barrels a day believed to be leaking and BP says it could take 48 hours to know if the system is working.
Meanwhile, President Obama arrived in Louisiana for his third visit to the region since the crisis began.
The visit to the Gulf area comes as beaches in the key tourist area of north-west Florida saw their first major signs of oil.
Adm Allen stressed that he could not give any certain figures on the amount being funnelled from the leaking well.
"Sometime later [on Friday] we'll probably be able to get an approximation of how much oil we are capturing," he said.
Adm Allen said that the amount should increase as BP shut off vents to capture more of the oil.
He added: "Progress is being made, but we need to caution against over-optimism."
But BP chief operating officer Doug Suttles said he was "pretty confident" the plan would work.
"It probably won't capture all of the flow. But it should capture the vast majority," he said.
BP says it has spent more than $1bn so far on the operation to contain the spill and clean up the oil.
In a conference call to investors, BP chief executive Tony Hayward said it could take 48 hours before the system was optimised and a determination made on whether it had succeeded.
He said BP was "heartbroken" by the loss of life, damage to the environment and impact on people's livelihoods caused by the spill.
Eleven workers lost their lives when the Deepwater Horizon drilling rig, leased to BP, exploded and sank in April.
The estimates for the amount of oil that has already leaked vary widely from 20 million to 45 million gallons.
BP had previously made a number of unsuccessful efforts to halt the leak and accepts it may not be fully contained until relief wells now being drilled become ready in August.
Mr Hayward said BP was working hard to rebuild the trust of the American people and to ensure such an event would never happen again.
He admitted that people wanted to know the cause of the disaster.
But he said it was a complex accident caused by an "unprecedented number of failures" and "a lot remains unknown".
He said a "separate stand-alone" organisation would be created within BP to deal with the Gulf of Mexico spill.
The company also said it would not make a decision on its next dividend payment until late July.
BBC economics correspondent Andrew Walker says if it does pay the dividend, this will go down very badly in the US, where pressure is mounting for BP to retain the cash for the clean-up.
President Obama is to meet Adm Allen, other officials, and members of local communities affected by the spill during his visit.
He told CNN on Thursday that BP had already "felt his anger" over the spill and that he was "furious at this entire situation".
Mr Obama has for the second time postponed a trip to Australia, Indonesia and Guam, in order to deal with the crisis.
The area affected by the oil slick continues to spread.
Tar balls have now begun to wash up on the beaches of Alabama and north-west Florida.
At Pensacola Beach in Florida, swimmers encountered an oil sheen and children picked up tar blobs as big as tennis balls.