Former foreign affairs minister Alexander Downer says China has developed a reputation for pursuing what one might call “hostage diplomacy”.

“That is that it’s a sort of tit-for-tat – they seize our people and they seize them until they achieve whatever they want to achieve,” Mr Downer told Sky News host Chris Kenny.

It comes after Australian citizen Cheng Lei was formally arrested in China after being detained for six months.

Foreign Affairs Minister Marise Payne confirmed Ms Lei was arrested last Friday, accused of illegally supplying state secrets overseas.

“They’ve done that with Canada,” Mr Downer said.

“They’ve held a Canadian citizen for a long time, for a couple of years now, in retaliation for the Canadians holding a Chinese citizen and prosecuting a Chinese citizen,” he said.

Mr Downer said the situation is “pretty serious” relating to Ms Cheng.