"I have issued a state of emergency to help local governments and state agencies work together more efficiently as they respond to this massive oil spill," he said. 

U.S. President Barack Obama on Friday ordered investigation into an oil rig explosion that led to a massive oil spill in the Gulf of Mexico, threatening fragile coastal environment there. [Xinhua]

Authorities have been trying to coordinate resources to avert what is likely to be one of the worst ecological disasters in U.S. history. The Pentagon also authorized the deployment of the Louisiana National Guard.

Fresh water was being diverted from the Mississippi River into ecologically important wetlands on the coastline in hopes that they may push back some of the oil.

The slick measured at least 1,500 square kilometers on Wednesday and grey patches can be seen clearly on satellite images taken Thursday.

With the leak no closer to being capped, many are now comparing the Gulf of Mexico oil spill to the grounding of oil tanker Exxon Valdez in Alaska in 1989. Eleven million gallons of oil leaked from the tanker at that time, making it the worst oil spill in U.S. history.

The Coast Guard said earlier that oil was leaking from the ruptured well at an estimated rate of 5,000 barrels (210,000 gallons or 794,900 liters) a day. At that rate, it takes less than two months for the amount of spilled oil to surpass that poured from the tanker Exxon Valdez.

The Coast Guard was coordinating vessels investigating the underwater damage of the Deepwater Horizon rig. The rig exploded on April 20 and 11 workers were missing. Officials found oil was leaking Saturday.

British Petroleum, which operated the deepwater rig, said it was taking full responsibility for the spill and would pay for legitimate claims resulting from the disaster.

Officials, however, have warned British Petroleum that its resources appeared insufficient to avert a major disaster as winds also helped push some of the oil towards the shore.

"I do have concerns that BP's resources are not adequate. I urge them to seek more help from the federal government and others," Lousiana Governor Bobby Jindal said.

British Petroleum has been operating 10 robotic submarines in an attempt to cap the ruptured well on the seabed some 1,500 meters below the surface, but it has so far been unsuccessful.