BP successfully cut the lower marine riser pipe at 10 a.m., using giant shears 5,000 feet below the surface of the sea, but it was a "more jagged cut" Coast Guard Adm. Thad Allen told reporters, and therefore will be a looser fitting seal.
Now a containment dome with a rubber seal will be lowered over the severed pipe. Allen called the cut a "significant step forward" and said the leak could be largely sealed today.
This morning Allen told "GMA" that he hopes they will begin funneling oil to the surface as early as today, a long as nothing goes wrong.
"They've got the top hat containment device positioned over the top of the well head. And they will be able to lower that down on a lower marine riser package as soon as they make that cut, and that's connected to a ship on the surface," Allen said on " GMA."
While the pipe was successfully cut this morning and BP hopes to start bringing the oil up today, Allen told "GMA" there could still be complications.
"We encounter technical difficulties in doing things on the sea floor at 5,000 feet that have never been attempted before in some cases," Allen said. "So they adapt. They learn and they keep moving on. They've got other devices that are a little larger in case the fit's not right."
BP had a setback Wednesday when the diamond saw made it almost halfway through the 20-inch pipe but then became stuck inside the riser pipe. It took 12 hours to get the blade out. BP abandoned the saw and switched to using gigantic robotic shears. Although the shears made an irregular cut, Allen told reporters he expects the seal to still be tight.
"We would have liked to have had the diamond cut ... because that gives you a smooth fitting that you can actually put a cap on ... with a rubber seal. This one is going to be a little looser fitting. There might be some oil escaping around the edges," Allen told "Good Morning America."
Once the new containment device is on, BP may need to go back down to make a cut with the diamond wire saw once it understands what is happening with the riser pipe, Allen said.
"For now, we need to contain this oil as quickly as possible," Allen said.
This is BP's seventh attempt at controlling the leak. Since it began the "cut and cap" operation Tuesday, oil has been gushing out an estimated 800,000 gallons per day, which is 20 percent faster than previously.
Oil has hit at least 125 miles of the Gulf Coast. A slick sheen is seven miles from Pensacola Beach, Florida, the Coast Guard said Wednesday. The oil is expected to make landfall on the Florida coast by the weekend. Allen said the Coast Guard has deployed resources to the Gulf Coast beaches and the "picket line" has been established.
"We are flying more boom back into Alabama this morning, and we have dispatched a group of Coast Guard cutters with skimming capabilities that are down there," Allen said. "We've got helicopters offshore that are doing surveillance, Coast Guard patrol boats we are using for command and control, working with vessels of opportunity -- these are local fishermen we have brought on board to help us."
"The only technology we've ever had to deal with blowouts very severe is ? a very small-scale nuclear device ? right on top of the oil column, [detonating it] to en capsulate the stuff because it turns the earth into glass," Matthew Simmons, an energy expert, said.
Both BP and Washington said a controlled nuclear blast is not on the table.
"Well, that hasn't been seriously briefed to me, George," Allen told "GMA's" George Stephanopoulos. "I think we have to run out of a lot of things before we consider something like that. I think that's really on the peripheral of things we ought to be talking about right now."
BP CEO Tony Hayward admitted to the Financial Times that BP "did not have the tools you would want in your tool kit" and said accusing the company of not being fully prepared was "an entirely fair criticism."
Hayward has been criticized for comments he has made, and Wednesday Louisiana Democrat Rep. Charlie Melancon called for Hayward to be removed and to bring in someone "that really wants to make sure the people of this state, the people of this Gulf Coast region, have what they need."
Allen said while there is "a lot of talk about trust and confidence," he said that is not his responsibility.
"My responsibility is that BP does what it is supposed to -- conduct the proper oversight and make sure they are responsible or accountable for doing that," Allen said. "I work continuously with Tony Hayward. I have and will continue [to] in the future. Right now, the No. 1 goal we have is to get this oil contained and to get this cleanup done for the American people."
Wednesday Hayward apologized in a Facebook post for a comment he made Sunday when he said he wanted to stop the leak because "I want my life back."
"I apologize, especially to the families of the 11 men who lost their lives in this tragic accident. Those words don't represent how I feel about this tragedy," Hayward wrote.
ABC News' Brian Hartman contributed to this report.
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