US President Barack Obama has described a sprawling oil slick in the Gulf of Mexico as a "potentially unprecedented" environmental disaster, BBC reported.
He was speaking in Louisiana, where he was holding crisis talks with officials to discuss how to tackle the crisis.
Louisiana Governor Bobby Jindal warned earlier that the spill - caused by the sinking of an oil rig - was threatening the "way of life" in his state.
A senior US official said it could take three months to contain the leak.
"You're looking at potentially 90 days before you ultimately get to what is the ultimate solution here and that's a relief well," Interior Secretary Ken Salazar told NBC's "Meet the Press."
Hopes are that such a relief well - which is already being drilled by British Petroleum - would divert the flow of oil from a ruptured well about 50 miles (80km) off Louisiana's coast.
The BP-operated Deepwater Horizon rig sank on 22 April, two days after a huge explosion that killed 11 workers.
Some 1.6m gallons (six million litres) of oil have spilled since the blast, the US Coast Guard says.
The well is spewing about 5,000 barrels of oil a day, according to some estimates. But officials admit that it is nearly impossible to be sure how much is leaking.
Forecasters said there would be no let-up on Sunday of the strong winds that have been pushing the oil towards the Louisiana shore.
The BBC's Andy Gallacher, who is in the area, describes two-metre high waves rolling in.
Commercial and recreational fishing from Louisiana to parts of the Florida Panhandle has been closed for at least 10 days, the National Oceanic and Atmospheric Administration (NOAA) has announced.
'BP will pay'
Mr Obama flew to Louisiana on Sunday to see for himself the devastation caused by the spill.
Speaking in the town of Venice, he said: "We're dealing with a massive and potentially unprecedented environmental disaster.
"The oil that is still leaking from the well could seriously damage the economy and the environment of our Gulf states. And it could extend for a long time. It could jeopardise the livelihoods of thousands of Americans who call this place home."
The president said the slick was now nine miles (14km) off the coast of south-eastern Louisiana.
He vowed to do "whatever it takes and as long as it takes" to contain the spill.
But he warned: "BP is responsible for this leak. BP will be paying the bill."
Mr Obama is being briefed by federal and state officials on what urgent steps need to be taken to tackle the disaster.
Mississippi, Alabama, Louisiana and Florida have all declared a state of emergency.
Attorneys general from these states were meeting to discuss legal options, as pressure mounts on BP.