The Helix Q4000 burns off collected oil at the site of the Deepwater Horizon oil spill in the Gulf of Mexico on Sunday. (Gerald Herbert/Associated Press)

Oil spewed unabated into the Gulf of Mexico for a second day as BP prepared a new cap for its damaged well, but the company said work was progressing faster than expected.

The oil flow increased Saturday after the older cap, which was installed June 4, was removed. That device allowed some crude to keep pouring into the Gulf. BP hopes the new, tighter cap will collect most if all of the oil.

The switchover, made possible by robotic submarines, should now be completed in three to six days, BP said.

While the oil continues to gush 1.6 kilometres under the water, BP is stepping up cleanup efforts on the surface, said company spokesman Mark Proegler.

BP said a third containment ship, the Helix Producer, will begin capturing some oil later Sunday.

"We'll be able to do record skimming and booming over the next day," he told CBC News, speaking from New Orleans.

Proegler said there are contingency plans in case the installation fails. He estimated there are up to seven different caps available on the ocean floor. But he said the cap chosen for the containment effort is likely to work because it will be securely bolted into place.

Hope for permanently plugging the leak still lies with two relief wells, the first of which is expected to be ready at the end of this month, a BP executive said Sunday.

"The anticipation is toward the end of July is when we will be able to intercept the Macondo well," Kent Wells, senior vice-president of exploration and production, told reporters.

With files from The Associated Press