By Leika Kihara

TOKYO (Reuters) - All Nippon Airways Co, which has the biggest fleet of Boeing Co's troubled Dreamliner jets, on Saturday cancelled hundreds of flights until February 18, signaling a quick fix to the plane's safety problems was unlikely.

ANA, Asia's biggest airline by revenue and an important launch customer for Boeing's newest plane, said another 379 flights scheduled for February 1-18 had been scrapped, bringing to 838 the number of cancellations since one of its Dreamliners made an emergency landing in western Japan on January 16.

The announcement underscores the widening pain the Dreamliner problem is inflicting on the industry, with safety regulators and experts warning that investigations into the cause of a series of small fires on the plane could take months or even a year.

All Dreamliners have been grounded since January 17, forcing hundreds of flight cancellations worldwide, including in the United States, India and South America.

The cancellations have affected more than 82,620 passengers for ANA, which says it flies around 3.7 million passengers each month on domestic and international routes.

ANA said in a statement it will make further announcements on what to do with flights beyond February 19.

The announcement came after U.S. safety regulators said they were nowhere near finishing a probe into a battery fire on one of the 787 aircraft, raising the prospect of a lengthy suspension for the cutting-edge airliner.

Japan's two big carriers -- ANA and Japan Airlines -- have been most affected because they own around half of the lightweight, fuel-efficient jetliners in operation as a strategic move to grab market share from their U.S. and European rivals.

The grounding is particularly hard on ANA, which acknowledges it may have to scale back its next 2-year business plan that puts the Dreamliner at the centre of its growth strategy.

"The 787, which is the pillar of our management strategy, is in such a condition we have yet to decide on whether we can present a 2-year plan like we did in the past," ANA spokesman Ryosei Nomura has told Reuters.

Investigations have centered on the plane's lithium-ion battery unit. U.S., Japanese and Boeing representatives have this week been at the Kyoto headquarters of GS Yuasa Corp, which makes batteries for the 787.

(Reporting by Leika Kihara; Editing by Paul Tait)