The union representing journalists in Australia issued a statement condemning the treatment of the two men and the "secret detention" of Lei.
China withdrew the press credentials of about a dozen journalists at the New York Times, Wall Street Journal and Washington Post.
Seven police officers entered his home, surrounding him and recording him on video as they read out a statement designating him a person of interest in a national security investigation, though he was not the subject of the case.
The Chinese Ministry of Foreign Affairs recently informed the USA embassy in Beijing of new curbs on foreign reporters "by denying them press card renewals and refusing to process pending visa applications for journalists who were expelled earlier this year", she said. Beijing said the move by Australia was "politically motivated".
The AFR quoted Smith as saying it was "great to be back home safely after a hard five days".
But he criticised the treatment of Chinese journalists in the United States, accusing Donald Trump's administration of taking them "hostage to pressure China".
According to his bio on ABC, Birtles is the ABC's China correspondent and has been based in Beijing since 2015.
Birtles told reporters at Sydney's airport that his departure was a "whirlwind and. not a particularly good experience".
"They're quite fortunate really to be out of there", he said of Birtles and Smith. To protect the citizens, the Australian government urged all the Australian journalists to return back to the country immediately.
This came after the Australian government advised Birtles to leave China.
Aussies to get free coronavirus vaccine from early next year
Earlier, Russia had said that it is planning to produce 6 million doses of coronavirus vaccine per month. The preliminary results of the Phase 3 trial will be published in October-November 2020", said Dmitriev.
Diplomats eventually brokered a deal that said they could leave the country in exchange for agreeing to be interviewed by police.
He then spent the next four days staying in the Australian Embassy in Beijing as Chinese officials demanded an interview.
"I believe the episode was more one of harassment of the remaining Australian journalists rather than a genuine effort to try and get anything useful for that case", he said from his Sydney quarantine hotel.
However, ministry spokesperson Zhao Lijian also accused the US of being "arrogant and unreasonable" in talks about the matter and "not addressing China's normal and reasonable concerns and demands at all".
Birtles said he knew Cheng, "but not especially well", and Smith had met her once in his life.
Tuesday was the first time that Chinese authorities have given any indication as to the nature of the investigation into Cheng.
The Australian's China correspondent, Will Glasgow, has been working for a short time in Sydney, having returned for family reasons.
"I hope that can be revised in a timely way".
It added that the incident was "regrettable and disturbing and is not in the interests of a co-operative relationship between Australia and China".
The Foreign Correspondents' Club of China said on Monday a record 17 foreign journalists were expelled from the country in the first half of 2020.
It has taken the extension issue and the Chinese journalists as hostages to exert maximum pressure on China. The trade barriers were thought to be retaliatory after Australian Prime Minister Scott Morrison called on world leaders in April to back an independent inquiry into China's handling of the Covid-19 outbreak.