Rice farmer Nguyen Hien Thien is so busy growing his crops that he has never even visited Can Tho, a town only a few miles from his farm in the southern Mekong Delta.

"When I was a child, we grew one crop of rice per year -- now it's three. It's a lot of work," 60-year-old Thien, who has been farming since he was a child, told AFP on the edge of his small paddy field.

Experts say Vietnam's drive to become one of the world's leading rice exporters is pushing farmers in the fertile delta region to the brink, with mounting costs to the environment.

The country is already the world's second largest exporter of the staple grain. But intensive rice cultivation, particularly the shift to producing three crops per year, is taking its toll on farmers and the ecosystem.

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