The department has tested the fruits grown in the two localities and granted regional codes for five areas that are qualified to export them to the US.
The longan grown on a trial basis for export to the US achieved 95% of the required quality, Hoang Trung, the department's deputy director, said.
Businesses are co-operating with the department's Import and Export Centre to go directly to these five areas to buy from farmers for the export, he said.
Hung Yen has 20 hectares of longan trees owned by 175 households in Ham Tu Commune of Khoai Chau District and Hong Nam Commune of Hung Yen City, which have been granted the codes.
The province, a traditional longan grower, has a total of 2,000ha under the fruit that yield 35,500-40,000 tonnes a year.
Farmers and farm workers in the approved areas have been given training and financial support for plant protection and fruit preservation to ensure optimum quality of the fruits to be exported.
Farmers are required to strictly follow Vietnamese Good Agriculture Practice (VietGap) standards like using only permitted bio-pesticides.
The US Department of Agriculture approved the import of fresh lychee and longan from Vietnam in 2013.
The fruits will be subject to a systems that includes treatment and inspection requirements and restrictions on distribution.
As a pre-condition for entry, the fruits must be grown in orchards registered with and monitored by the National Plant Protection Organisation of Vietnam to ensure they are disease-free.
The fruits should also undergo irradiation to neutralise plant pests. For the first time this year Vietnam shipped lychee and longan to the US which has tough quarantine regulations for fruits.
Vietnam hopes to export 600 tonnes of lychee and 1,200 tonnes of longan to the US every year.