A court in Hanoi has begun hearing an appeal from a prominent blogger who was sentenced earlier this year to five years in prison for anti-state writings.

Nguyen Huu Vinh, better known as Anh Ba Sam, was convicted of abusing democratic freedoms to infringe on the interests of the state at a one-day trial in March.

Vinh's colleague Nguyen Thi Minh Thuy, who was given a three-year jail term on the same charge is also appealing her sentence.

Security around the Higher People's Court near downtown Hanoi, was tight with roads blocked off.

New York-based Human Rights Watch has called for the release of both defendants.