Ship fire

The speech comes as the blown-out BP well gushed crude oil for a 57th day, creating an unprecedented environmental and economic disaster.

IN DEPTH

Earlier this month, BP began its "top hat" containment procedure, which involves a cap placed over the leak that gathers the oil, allowing it to be siphoned up via a pipe to a container ship.

BP said that a bolt of lightning had struck the ship capturing oil from the well on Tuesday, igniting a fire that halted containment efforts.

The fire occurred on the Discoverer Enterprise, where engineers had been siphoning about 2.4m litres of oil a day.

"At the moment, there's no capture, no containment going on, but we'll start up the Enterprise when it's safe to do so," said Robert Wine, a BP spokesman said.

The company will use robotic submarines to survey the entire containment system, including the cap over the well, for possible damage from the fire.

Financial hit

Obama's speech comes on the same day that executives from BP and other major oil companies such as Exxon Mobil, Chevron, ConocoPhillips and Royal Dutch Shell, were defending their drilling practices at a congressional hearing in Washington.

The accusations of choosing cost saving over safety come as BP, a listed company which has lost about half its market value since the spill began almost two months ago, was stripped of its AA debt rating by Fitch, a ratings agency.

The downgrade follows a precipitous 9 per cent fall in BP's shares on Monday after more than 50 Democratic senators proposed that the company make a $20bn payment into an independently managed account to cover compensation for victims and the clean-up.

US politicians have also been calling on BP to scrap its quarterly dividend to ensure it has enough money on hand to cover any costs.

BP shares trading in London closed down 5.52 per cent at 342 pence on Tuesday.

BP meeting

The April 20 explosion on an offshore rig killed 11 workers and ruptured BP's well.

The spill has fouled 190km of US coastline, imperilled the multibillion-dollar fishing and tourism industries and killed birds, sea turtles and dolphins.

The oil gusher, 1,600 metres deep in the Gulf, which the US government does not have the technology to stop, has forced Obama and the federal government to rely on BP for an eventual fix.

That is not likely to happen until a relief well penetrates the blow-out in a couple of months.

The president's first televised Oval Office address is aimed at showing his deepening involvement in tackling the crisis, in the face of criticism among some Americans that he reacted too late.

The disaster has cut severely into Obama's schedule, including threatening his legislative agenda on such issues the overhaul of financial regulation, climate change and immigration reform.

On Wednesday, Obama will meet BP executives at the White House to discuss damage claims and the next steps in stopping the leak.