U.S. President Barack Obama toured Louisiana on Friday to get a first-hand look at the impact of the massive oil spill in the Gulf of Mexico.

The president arrived by plane in New Orleans in the mid-morning before boarding a helicopter with U.S. Coast Guard Admiral Thad Allen, who is overseeing cleanup operations in the Gulf.

U.S. President Barack Obama, left, picks up a tarball as LaFourche Parish president Charlotte Randolph looks on during a tour Friday of areas affected by the Gulf of Mexico oil spill. (Evan Vucci/Associated Press)

They flew to Port Fourchon, in southeastern Louisiana, where thick oil threatens the sands of Fourchon Beach.

A shirt-sleeved Obama walked to the water's edge, stooping as Allen explained what he was seeing. It is Obama's second visit to the region since the disaster began.

The beach, sealed off with crime-scene-style yellow tape, is one of the few sandy stretches on Louisiana's coast, which is mostly marshland. Obama called reporters travelling with him to the water's edge to point out some small tar balls.

"These are the tarballs that they're talking about," he said. "You can actually send out teams to pick up as they wash on shore."

Obama received a formal briefing by Allen in nearby Grand Isle, La., and later told reporters that he made it clear that the admiral should get whatever resources required to deal with the crisis.

Obama also vowed continued support for affected area residents.

"You will not be abandoned. You will not be left behind," he said. "The cameras at some point may leave. The media may get tired of the story, but we will not. We are on your side and we will see this through. We're going to keep at this every day until the leak is stopped, until this coastline is clean and your communities are made whole again. That's my promise to you."

BP admits failure

The head of BP acknowledged earlier Friday that his company failed in its efforts to protect the shoreline along the Gulf of Mexico, calling the impacts of the massive oil spill an environmental "catastrophe."

"It is clear that we're dealing with a very significant environmental crisis and catastrophe," CEO Tony Hayward told CNN's American Morning on Friday.

"A cup of oil on the shore is failure," he said, referring to the thick, gooey oil washing up in the marshlands and shores of Louisiana. "In that regard, we have failed to defend the shoreline to the degree and extent that we believed we could."

Drilling mud escapes from the broken pipe on the gushing oil well in the Gulf of Mexico early Friday morning. (BP PLC/Associated Press)

BP's latest attempt to stop the oil flow is "proceeding broadly according to plan," Hayward said, adding it could be 48 hours before the company knows conclusively if it is working.

After an 18-hour delay Thursday to assess its efforts and bring in more materials, BP resumed pumping heavy drilling mud into the blown-out well 1,500 metres underwater in a procedure known as a "top kill."

It also conducted a "junk shot" by injecting small, dense rubber balls and rubber scraps into a series of valves at the top of the wellhead, called the blowout preventer, to clog it up and keep mud from escaping.

An underwater video of the pipe shows some of the light brown mud gushing out of the same holes the much darker oil used to gush from.

The mud is non-toxic, water-based and "does no environmental harm at all," Hayward said.

The top kill is the latest in a string of attempts to stop the oil that has been spewing since the drilling rig Deepwater Horizon exploded April 20, killing 11 workers.

If the procedure works, BP will inject cement into the well to seal it permanently. If it doesn't, the company has a number of backup plans. Either way, crews will continue to drill two relief wells, considered the only surefire way to stop the leak.

With files from The Associated Press