Three Australians were detained and released from China's political re-education camps in Xinjiang province in the past year, according to the Department of Foreign Affairs and Trade (DFAT).

Key points: Australia has approached China on behalf of people seeking missing relatives

Australia has approached China on behalf of people seeking missing relatives A senior DFAT official says reports 1 million Uighurs have been detained are "credible"

A senior DFAT official says reports 1 million Uighurs have been detained are "credible" China has blocked Australia and foreign diplomats from visiting Xinjiang

"We only found out about that after they had left Xinjiang," Graham Fletcher, the head of DFAT's North Asia division, told a Senate Estimates Committee in Canberra on Thursday.

"Those three individuals are now back in Australia so they're okay."

Australian Government sources have told the ABC that some Uighurs who live in Australia, but who are not citizens, have also been detained in Xinjiang.

It is not clear how many of them are still in detention, and their identities have not been made public.

An estimated 1 million Uighur Muslims have been detained in camps across Xinjiang as China steps up efforts to control the Uighur population, according to several reports this year.

Australia is home to a tight-knit Uighur community of an estimated 600 families, with a combined population of over 3,000 people.

Most Uighurs live in Adelaide, with other Muslim minorities who have also been targets of the crackdown.

Australian officials have fielded multiple requests for help from Australian residents concerned about missing relatives in Xinjiang.

Mr Fletcher said diplomats had contacted Beijing on behalf of two of those people: one who had lost contact with a single family member, and another who was searching for about 20 friends and relatives.

Canberra said it handed the names and locations of the people who could not be reached over to the Chinese Government.

"The response was that we haven't supplied sufficient information," Mr Fletcher said.

"I think we need to consider what action, if any, we're prepared to take as a next step. We haven't done that yet."

China blocking Australian diplomats from Xinjiang

The United Nations has cited estimates that 1 million Uighurs have been detained in political re-education camps. ( Reuters: Thomas Peter )

Mr Fletcher said reports Australia's biggest trading partner was detaining up to 1 million Uighur Muslims in re-education camps were "credible" but it was unclear exactly what was transpiring in Xinjiang.

"There seems to be a fairly widespread incidence of individuals being detained for periods for re-education and indoctrination," he said.

"They call it vocational training and frankly we don't know enough about it to be able to say whether that is an element of it or not, but it seems to be designed to reinforce the Chinese Government's priorities in relation to ethnic relations in Xinjiang [and] civil order."

According to Mr Fletcher, China is preventing Australian and other foreign diplomats from assessing the situation.

Australian officials last travelled to the province in north-western China at the beginning of 2017.

Since then, Mr Fletcher said, a number of requests to visit the province had been knocked back.

"We have expressed to China at a national level our interest in visit Xinjiang," he said.

"We continue to seek approval."

In response to a request for comment, the Embassy of China in Australia referred the ABC to a Chinese state media interview with a high-ranking Xinjiang government official who defended the camps as "vocational training centres".

China has repeatedly said the measures it is taking in Xinjiang are designed to eliminate "extremism, terrorism and separatism" among the Uighur community.