US President Barack Obama has arrived in Louisiana saying an oil slick in the Gulf of Mexico, which is threatening the US shoreline, is potentially an unprecedented environmental disaster.
Speaking to reporters in the small fishing village of Venice, Mr Obama said the British oil giant, BP, was responsible for the leak and will be paying the clean-up bill.
But he added that the US would be doing all it could to assist the operation.
Earlier, US Interior Secretary Ken Salazar said it could be up to 90 days before a relief well is completed to address the spill.
Oil is continuing to leak from a sunken BP rig and has started washing ashore, threatening an economic and ecological catastrophe.
US officials have closed commercial and recreational fishing for a minimum of ten days in affected federal waters.
The affected waters are largely between Louisiana State waters at the mouth of the Mississippi River to Florida's Pensacola Bay, the US National Oceanic and Atmospheric Administration said.
Choppy seas and strong winds have been hampering the clean-up operation.
Mississippi, Alabama, Louisiana and Florida have all declared a state of emergency.
Mr Salazar said BP would have to fulfil its responsibilities to monitor the rig and prevent further oil spills.
The Deepwater Horizon rig, owned by Transocean, sank on 22 April, two days after it exploded and caught fire while finishing a well for BP almost 70km off the Louisiana coast.
11 workers are missing and presumed dead after the rig exploded.
