Energy giant BP reported a limited success at containing the oil that is gushing into the Gulf of Mexico last yesterday, but a sceptical US government said it was "not a solution".
Crude oil has been flowing unchecked from a ruptured well about 1.6km under the ocean's surface, threatening an ecological and economic calamity along the US Gulf Coast.
The company said it will try to fully stop the flow later this week. BP said 1,000 barrels a day of the oil spill were being captured on the surface by a drill ship.
"This is just containing the flow, later this week, hopefully before the end of the week, we'll make our next attempt to actually fully stop the flow," BP Chief Operating Officer Doug Suttles said.
After other attempts to contain the spill failed, BP succeeded in inserting a tube into the leaking well and capturing some oil and gas.
The underwater operation used guided robots to insert a small tube into a 21-inch 53-cm pipe, known as a riser, to funnel the oil to the drill ship at the surface.
"It's working as planned and we are very slowly increasing the rate that is coming from the riser tool up to the surface," BP senior executive vice president Kent Wells told reporters.
US government officials and lawmakers downplayed the significance of BP's latest breakthrough.
"This technique is not a solution to the problem, and it is not yet clear how successful it may be," secretary of Homeland Security Janet Napolitano and secretary of the Interior Ken Salazar said in a joint statement.
"I don't think we should get our hopes up until we know for sure that all of the oil is staying down," said Edward Markey, a Democratic congressman from Massachusetts.
"With reports of miles-long undersea clouds of oil floating around the Gulf of Mexico, and the very real possibility that more oil has been spilt than previously estimated, this crisis is far from over," he said.
BP's best near-term hope of stopping oil from pouring from the well is "kill mud," a heavy mixture of synthetic materials that technicians will attempt to shoot into the well to form a barrier to prevent oil and gas from escaping.
If the mud fails to seal the well, BP will try to inject golf balls, tire fragments and other materials into the well to clog it up - known in the industry as a "junk shot."
The limited success yesterday followed a previous setback, when a cord taking the oil to the surface became entangled.
BP's earlier attempts to contain the leaking well have been stymied by the technical difficulties of working in the sea floor's cold, dark conditions.
On May 7th, BP tried to lower a containment dome over the leak, but the 100-tonne device was rendered useless by a slush of frozen hydrocarbons that clogged it.
The spill began after an April 20th explosion on the Deepwater Horizon rig that killed 11 workers. It threatens to eclipse the 1989 Exxon Valdez spill off Alaska as the worst US ecological disaster.
BP, under heavy political pressure as a result of the spill, has a "systematic safety problem" at its oil refineries, a US Labor Department official told the Financial Times.
Last year US safety regulators hit BP with a record $87.4 million fine for failing to fix safety violations at its Texas City refinery after a deadly 2005 explosion.
Reuters