UPDATE 1-Oil leak from ConocoPhillips' China field cleaned up

(Adds CNOOC's statement confirming oil slick cleaned up)

* Leak occured earlier in June, oil slick cleaned up - CNOOC

* Production of Penglai 19-3 oilfield little affected - sources (Adds details)

BEIJING, July 1 (Reuters) - A small oil leak from the Penglai 19-3 oilfield off China's Bohai Sea, operated by U.S. firm ConocoPhillips , has been largely cleaned up, with production barely affected, Chinese partner CNOOC Ltd and industry sources said on Friday.

The Penglai 19-3 field is China's largest offshore oilfield, with daily production of roughly 160,000 barrels. ConocoPhillips holds a stake of 49 percent in the project while China's CNOOC Ltd has 51 percent.

"Not much oil was spilled, but the reaction to cope with the spill was a bit slow. The clean-up has largely been completed about a week earlier," said one industry official with knowledge of China's oil production at Bohai Sea.

"We understand the incident may have had a very small impact on the production," said a trading source familiar with cargo flows of the Penglai crude. "It may incur a few days of delay in crude loadings, but that's it."

CNOOC Ltd confirmed the leak that occurred earlier in the month that caused an oil slick near the waters of Penglai 19-3 field.

"The leaking points have long come under control and the oil slick has basically been cleaned up," Jiang Yongzhi, CNOOC Ltd's spokesperson said in an email, adding the cause of the spill was being investigated.

The Southern Weekend newspaper reported on Thursday that the incident started around June 10 and oil spilled from two points including one from Platform B, one of Penglai's five production platforms.

An oil slick 3-km long and 20 to 30 metres wide was found floating near the field, but it was soon cleaned up, the paper said.

An official with the State Oceanic Administration said the agency would hold a news conference on July 5 about the incident, but made no further comment.

Penglai crude is a heavy grade used mostly to feed the Huizhou refinery in China's southern province of Guangdong owned by CNOOC Ltd's parent.

The field has a 2 million-barrel floating, production, storage and offloading facility, the largest in China, which normally can provide a supply cushion in case of an emergency production shutdown.

Last July, a pipeline explosion at Dalian, one of China's largest ports, triggered a major offshore oil spill and disrupted cargoes for almost two weeks.

(Reporting by Chen Aizhu and Judy Hua; Editing by Clarence Fernandez)