HANOI, VIETNAM: Vietnam has freed a detained blogger and a journalist who were critical of government policies towards China and involved in a plan to distribute anti-China T-shirts, the blogger and a lawyer said on Sunday. The releases came ahead of a Sept. 6-9 visit by Communist Party chief Nong Duc Manh to Australia and New Zealand, where he is sure to face protests and pressure over human rights.

Hanoi police told Bui Thanh Hieu on Saturday evening he was being freed because of "the cancellation of preventative measures" on him, said Hieu, who spent nine nights in detention.

"I don't know exactly why they freed me," said Hieu, who blogs under the name "Nguoi Buon Gio", or Wind Trader.

Pham Doan Trang, a journalist for the highly popular news website VietnamNet, was released on Friday evening, said lawyer Cu Huy Ha Vu. Vu said he had been in direct contact with Trang, who was detained a day after Hieu.

The blogger confirmed he had been detained in connection with a plan to print and distribute to major Vietnamese cities T-shirts opposing China's involvement in a bauxite mining scheme and claims over disputed islands in the South China Sea.

The arrests have underscored how sensitive Vietnam's relations with China are while highlighting the challenge Hanoi faces in keeping public opinion in check as Internet usage blossoms -- and where it draws a line on organised dissent.

The bauxite issue came into the spotlight last year when war hero Gen. Vo Nguyen Giap urged the government to reconsider it. Opponents of the plan say it will damage the environment and contend that China's involvement is a national security risk.

Analysts say the Party has in the past freed high-profile political prisoners or detainees ahead of major visits.

Vietnam's relationship with China is laden with baggage from centuries of conflict, and the Vietnamese Communist Party performs a delicate balancing act between the need to stay on good terms with China and a populace that is highly suspicious of the giant neighbour to the north.

Analysts say the Chinese government is not shy about putting pressure on Vietnam to keep media and bloggers on a tight leash when it comes to criticism about China.

Another person who was arrested last week also in connection with the T-shirt scheme, blogger Nguyen Ngoc Nhu Quynh from the southern beach town of Nha Trang, was not released, her mother said by telephone on Sunday.

Hieu said he, Trang and Quynh had been "close friends" for a long time, but he would did not say if the other two were involved in the T-shirt scheme.