HANOI (Reuters) - Tropical storm Gaemi is forecast to slam into Vietnam's central coast later on Saturday, dumping heavy rains and strong winds in the Central Highlands coffee belt, which could result in a decline in output, the government and traders said.

The storm, the seventh to hit Vietnam this year, would be centered near the coastal provinces of Binh Dinh and Phu Yen, with winds travelling at up to 74 km (46 miles) per hour, a government statement said.

It would weaken after landfall and move further west by Sunday, dumping wind and heavy rains in the northern part of the Central Highlands while en route to Cambodia, the statement said.

"Rain may not harm coffee cherries now but strong wind can cause young cherries to drop," said a coffee trader from Daklak, the country's largest coffee growing province and one of the five provinces in the Central Highlands.

The northern part of the region includes the provinces of Kontum and Gia Lai, which are the smallest in terms of coffee areas among the five, ranking after Daklak, Lam Dong and Dak Nong.

Around 80 percent of Vietnam's coffee comes from the region, where harvesting of the new 2012/2013 crop will begin in 10 days, with output initially expected to ease 7-10 percent from a record high 1.6 million tonnes in the previous 2011/2012 season.

A larger decline could tighten supply from the world's largest robusta producer, putting pressure on prices. Demand for robusta is expected to be strong in the current season, with steady buying seen in Europe's market this week.

Vietnam, with a north-south coastline, is widely exposed to storms and typhoons. More than 200 people have been killed or missing in the first nine months due to natural disasters including floods and landslides, government data show.

(Reporting by Ho Binh Minh; Editing by Sanjeev Miglani)