Vietnam will free nearly 3,800 prisoners including foreigners in the country's latest amnesty, the government said on Monday.

Vietnam has announced nine special amnesties since 2009, freeing more than 92,000 prisoners ahead of their expected release dates but always excluding political activists.

Those convicted for "attempting to overthrow" the communist government or "terrorism" are not eligible for release, according to Monday's official amnesty announcement.

This year, 3,765 detainees will be released including around 20 foreigners from Cambodia, China, Iceland, India, Laos, South Africa and the United States.

They are expected to be released on Tuesday in a belated move following Vietnam's September 2 National Day.

The amnesty comes after the early release mid-September of two high-profile detainees, as the country's top leader To Lam headed to the US.

Environmental activist Hoang Thi Minh Hong was serving a three-year jail term for tax evasion offences related to her environmental campaign group CHANGE.

Political dissident Tran Huynh Duy Thuc was an internet entrepreneur sentenced to 16 years in jail in 2010 for allegedly trying to overthrow the regime.

Officials on Monday refused to reveal the total number of prisoners currently in detention.

In August, authorities said around 643 foreigners are serving jail terms in Vietnam.

Human Rights Watch says more than 160 political prisoners are behind bars.

(AFP)

This picture taken on November 16, 2017, shows an inmate sitting on his bunk bed in a dormitory before lunchtime inside a drug rehabilitation centre in the northern city of Hai Phong. (AFP)

Vietnam to free nearly 3,800 prisoners in amnesty