(Adds troops start evacuating people in Bicol, Arroyo comments)

By Manny Mogato

MANILA, Nov 22 (Reuters) - The Philippines began evacuating tens of thousands of people from coastal areas in the central Bicol region as typhoon Mitag gathered strength, officials said on Thursday.

The Philippines is trying to avoid a repeat of last year's devastating typhoon Durian, which killed 1,200 people and left 120,000 homeless when it crashed through Bicol, the country's typhoon alley.

Glenn Rabonza, the head of the civil defence office, said about 10,000 people living on the slopes of Mayon volcano in Bicol had already been evacuated and the number was expected to rise to 50,000 in the next 24 hours.

"We're worried about the huge amount of volcanic debris that might be re-mobilised and eat up communities along the slopes of Mount Mayon," Rabonza told reporters, adding it could also generate storm surges.

"Coastal villages could be slammed by big waves as high as 3 to 10 metres whipped up by strong winds brought by the typhoon."

Mitag, currently a category 1 typhoon with winds of 120 kph (75 mph) and gusts of up to 150 kph (95 miles), is expected to make landfall either late Saturday or early Sunday.

Ahead of the storm, workers dismantled advertisement billboards placed along Manila's major roads. Many such billboards collapsed during a storm last year, killing several people.

At 10 a.m. (0200 GMT), Mitag was estimated at 490 km (300 miles) east of the central island of Catanduanes, moving westward at 15 kph (9 mph).

Mitag follows storm Hagibis that caused landslides, flooding and destruction of property, infrastructure and farmlands worth about $1 million.

Hagibis is currently over the South China Sea and moving west towards Vietnam after killing 13 people in the central and southern Philippines.

(Reporting by Manny Mogato, Editing by Sanjeev Miglani)

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