A Christian lawyer has been assaulted after attending a controversial human rights event in Vietnam, according to religious freedom charity CSW.

Nguyen Van Dai attended a forum on Sunday that sought to educate Vietnamese citizens about their rights, including the freedom of religion or belief, which police had requested be cancelled. Although the event ran without interruption, Nguyen was severely beaten shortly after leaving.

"Mr Nguyen and his friends travelled to Quan Hanh, the capital of Nghi Loc District," read a statement from Christan Solidarity Worldwide, a religious freedom charity.

"Upon their arrival they were met by approximately 20 plain-clothed police, who proceeded to confront them and beat them with wooden sticks, striking their shoulders and thighs.

"Mr Nguyen was pulled onto a motorcycle and driven to a different province about 20km from Nghi Loc, where the beatings continued and he received a blow to the head," the statement continued.

"Mr Nguyen's possessions were confiscated, including documents, his phone, camera and wallet. His jacket and shoes were also taken from him and he was pushed into the cold sea."

He was finally able to borrow a phone and call for help.

Vietnam has strong traditions of Confucianism and Taoism as well as Buddhism. However there is also a significant Catholic population.

Ahead of last weekend's conference there were several reports of freedom of religion or belief violations, according to CSW, which has called for an immediate investigation into the attack.

"Human rights defenders, including those who promote the right to freedom of religion or belief, deserve our unequivocal support," said CSW chief executive Mervyn Thomas.

"We call on the Government of Vietnam to protect the rights of individuals like Dai and his colleagues, and to allow them to carry out their vital work without interference or threats to their personal safety."