Two Australian journalists fled China yesterday under diplomatic protection, fearing arrest as political pawns in the rapidly worsening relationship between Canberra and Beijing.

Their dramatic overnight exit followed days of secret wrangling that had seen both men holed up in Australia's diplomatic missions to escape the clutches of China's security police.

Bill Birtles and Michael Smith had to consent to questioning before they were allowed to leave, shepherded on a late-night flight by Australian diplomats.

Both men were quizzed about fellow Australian journalist Cheng Lei, who has been detained since last month.

Beijing acknowledged yesterday that CGTN news anchor Cheng was being held on national security grounds.

Birtles, who works for public broadcaster ABC, said his interrogation in a hotel room had touched on Cheng's case, but that he did not think that was its primary objective. "I believe that the whole episode was really one more of harassment of the remaining Australian journalists, rather than a genuine effort to try and get anything useful for that case," he said.

China confirmed the two men had been questioned. "As long as foreign journalists obey the law they have no reason to worry," foreign ministry spokesman Zhao Lijian said.

The episode began when police carried out midnight raids on Birtles' home in Beijing and Smith's in Shanghai. Both were barred from leaving the country.

Fearful of interrogation and arbitrary arrest, they fled to the closest Australian diplomatic missions until agreeing to answer Ministry of State Security questions in return for safe passage home.

Michael Smith, left, and Bill Birtles arrive in Sydney under diplomatic protection. AP

Oz journos flee China after raids