Cheng was detained in August last year, but China's decision to arrest her signals the start of formal criminal investigation.

Foreign Minister Marise Payne said the process could take up to seven months.

"We will continue to provide the strongest possible consular support to her and engage as strongly as we are able to with Chinese authorities in relation to her detention," she told reporters in Sydney on Monday.

Senator Payne said Australia had consistently raised strong concerns about Cheng's detention at the most senior levels.

"We continue to seek assurances of her being treated appropriately, humanely and in accordance with international standards," she said.

Embassy officials have visited Cheng six times since her detention, most recently on January 27.

The Australian government was informed of her arrest on Friday night through its embassy in Beijing.

"Our thoughts are with Ms Cheng and her family during this difficult period," Senator Payne said.

Cheng's two young children are being cared for by their grandmother in Melbourne.

Her niece Louisa Wen, speaking on behalf of the family, said the children were devastated by their mother's absence.

"I feel like the children don't fully understand the situation, so it's probably quite tough on the kids wondering what's going on," she told the ABC.

"Every time we do something fun, we're thinking of her and how she can't enjoy these things with us."

Cheng was born in China but moved with her parents to Australia as a child.

She studied commerce at the University of Queensland before working for Cadbury Schweppes and ExxonMobil in Australia.

After moving to China, she worked as a high-profile business anchor on a state-owned television network.

Videos of Cheng were removed from Chinese websites after she was detained.

The Chinese foreign ministry initially said Cheng was suspected of endangering national security.

Former foreign minister Alexander Downer said it appeared to be retaliation by China, rather than a case of credible charges.

"As a journalist, what access to state secrets would she have?" he told the ABC.

"Journalists get leaks from time to time, but ... she has been accused of spying and I think that is just improbable and not credible myself."

Two other Australian journalists were banned from leaving China until they answered questions about Cheng.

Chinese police told the men they were people of interest in the case and both journalists were ordered to report for questioning.

The pair managed to flee the country after agreeing to be interviewed, sheltering in Australian diplomatic compounds until their safe passage could be secured.

Their hasty departures left Australia without any credentialed journalists on the ground in China for the first time in 50 years.

Australian Associated Press