An Australian writer and blogger feared to have been taken into custody by Chinese authorities has contacted friends and family to reassure them he is safe, reports said on Wednesday.

Australia's foreign ministry is urgently trying to trace Yang Hengjun, a former Chinese diplomat who is now based in Sydney and is an Australian citizen.

Yang had last been heard from on Sunday when he rang a colleague to say he was at Guangzhou airport in southern China and was being followed by three men.

"We are aware Dr Yang spoke to his family on 30 March, 2011 to say he was well," a spokesman for Australia's Department of Foreign Affairs and Trade was quoted as saying by the AAP news agency.

"We are seeking urgently to speak to him directly to confirm his situation."

Rights group Amnesty International has said those close to Yang believe he is being held by Chinese authorities.

Australian broadcaster the ABC reported on its website that Yang had made contact with friends, telling them the reason he had been out of contact is that he had been sick and because of problems with his mobile phone.

But one person who spoke to Yang told the ABC he "sounded very strange" when he said it, the broadcaster reported.

"Yang Hengjun's disappearance is extremely worrying, especially as it comes during one of the biggest round-ups of activists and critics for years," said Amnesty's deputy director for the Asia Pacific, Catherine Baber.

"He joins a long list of peaceful reformists who have gone missing or been arrested in China in the last month."

At a foreign ministry briefing in Beijing on Tuesday, a Chinese government spokeswoman said she had not heard of Yang and had no information about him.

Australia's foreign ministry said the government was urgently seeking to confirm his whereabouts and well-being.

Australia's Consul-General in Guangzhou has raised the matter with provincial and municipal-level Chinese authorities, while the Department of Foreign Affairs had spoken with the Chinese embassy in Canberra, it said.

Rights groups say Chinese authorities have been on edge since calls for protests emulating those sweeping the Arab world began in February and have since warned, placed under house arrest or detained up to 100 activists.

On Tuesday, China formally charged two activists on charges of "inciting subversion" amid the widening crackdown, which some say is the harshest in 15 years.

"There is no sign of this crackdown easing," Baber said, adding that Amnesty feared Chinese authorities were moving to treat any peaceful expression of support for reform as subversion.

burs-ft/apj

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