HOUSTON - An undersea accident forced BP Plc to shut down a critical system capturing oil from its leaking Macondo well early on Wednesday, unleashing a torrent of oil, the top U.S. oil spill official said.

A containment cap that channeled 16,600 barrels of oil to a drillship at the water's surface on Tuesday was removed after an undersea robot apparently hit it, Coast Guard Admiral Thad Allen said at a news briefing in Washington.

The system could restart later on Wednesday, he said.

Meanwhile, oil was gushing unchecked from the opening that the cap covered, Allen said, he said. A second oil-capture system was operating normally, pulling more than 10,000 barrels a day to the surface and burning it off.

A team of U.S. scientists estimates the leak is spewing up to 60,000 barrels a day.

Allen also reported two deaths of workers helping with the oil spill response. The deaths did not appear work-related but were under investigation, he said.

Allen said BP shut down the system when workers thought "some kind of gas" rose through a line that channels warm water to the cap to maintain temperature control.

The company said in a statement that a valve in that line spewed a liquid on the drillship, Transocean Ltd's Discoverer Enterprise.

ROBOT HIT CAP

Allen said the robot apparently hit the top of the cap, closing one of three open vents through which oil and gas had continued to leak. That could have created pressure that caused the problem with the water line, he said.

BP removed the cap to assess its condition. "They are checking the containment cap right now," Allen said.

The company intends to reinstall the cap on a pipe remnant that juts from the top of failed blowout preventer equipment at the seabed, he said.

Hours before Allen disclosed the cap removal, BP said both the oil-capture systems collected or burned off 27,100 barrels of oil on Tuesday, the highest capture rate yet.

The containment cap system installed June 3 captured 16,600 barrels, while a second system started up June 16 burned off 10,500 barrels, BP spokesman David Nicholas said.

Tuesday's overall capture rate was 900 barrels away from the total oil-handling capacity of 28,000 barrels, according to BP figures. The combined systems have collected a total of 325,700 barrels of oil, BP said.

While the cap system channeled oil to the drillship through a pipe, the second system was pulling more oil through a hose and pipe connected to the blowout preventer.

Allen said that "potentially next Tuesday" another rig, the Helix Producer, will join the setup to increase oil-handling capacity to up to 53,000 barrels a day.

"That's notwithstanding the removal of the containment cap today," he said.

That system will siphon oil through a second hose connected to the blowout preventer through a floating pipe to the Producer. He said the floating pipe has been installed and is being tested.

The floating pipe will allow the Producer to quickly disconnect and move if a hurricane approaches, Allen said.

The Enterprise and Q4000 have fewer hurricane-ready hookups and require more time to disconnect and move. And if seas grow rough enough for eight-foot (2.4 metre) waves, the vessels' effectiveness "becomes marginal as well," Allen said.

The National Hurricane Center said on Wednesday that a tropical wave south of Haiti in the central Caribbean Sea strengthened overnight and had a 30 percent chance of developing into a tropical depression over the next two days.

Most weather models project the system will move toward Mexico's Yucatan Peninsula. A couple of models showed it turning north toward the U.S. Gulf Coast states of Louisiana, Mississippi and Alabama where oil spill operations are in full force. (Reporting by Kristen Hays, Editing by Doina Chiacu and Alan Elsner)