UPDATE 1-BP capturing 5,000 bpd oil at Gulf leak site

* BP stock higher in down market

* Company says 5,000 bpd estimate is NOAA's (Adds detail, additional quotes from BP)

HOUSTON May 20 (Reuters) - BP Plc (BP.L) said it is now siphoning 5,000 barrels (210,000 gallons/795,000 liters) per day of crude oil at the leak site in the U.S. Gulf of Mexico.

BP had estimated the leak was flowing at a rate of 5,000 barrels per day, but scientists and the government have questioned that figure.

"It's now capturing 5,000 barrels per day of oil," BP spokesman Mark Salt, said.

Previously, the company said it was capturing 3,000 barrels (126,000 gallons/573,000 liters) per day.

The estimate of the leak's flow initially came from the National Oceanic and Atmospheric Administration and was an uncertain number, Salt said.

"Whatever the number, people can see we're trying to contain the flow and stop the spill," the spokesman said.

Steve Wereley, associate mechanical engineering professor at Purdue University, has pegged the spill's volume at about 70,000 barrels (2.9 million gallons/11 million liters), per day, based on data gleaned from a segment of video provided by BP.

"This is not rocket science," Wereley told a U.S. congressional panel on Wednesday. "All outside estimates are considerably higher than BP's."

BP has inserted a tube into a riser, or pipe, that is leaking oil from the sea floor. The company is gathering the crude oil and siphoning it up to a drill ship for storage.

BP depository receipts traded on the New York Stock Exchange rose 8 cents to $45.35, outperforming broad declines in energy shares.

(Reporting by Anna Driver in Houston, Editing by Sandra Maler)