Investor confidence in Vietnam's dong remains "fragile" and restoring it requires a consistent policy from Vietnam's government, Tomoyuki Kimura, the Asian Development Bank's country director for the Southeast Asian nation, said at a conference on Wednesday in Ho Chi Minh City.

The dong "may come under downward pressure" as foreign exchange borrowings mature toward the end of this year, Kimura said.

Vietnam's foreign exchange reserves were US$15.2 billion at the end of June, he said, covering 2.1 months of imports.

The reserves may exceed $15 billion, according to Andy Ho, the chief investment officer of VinaCapital Investment Management Ltd.

"Reserves have been growing quite nicely," Ho said on Wednesday.