Chinese officials have confirmed a third Canadian was being held for "unlawfully working in China".
Foreign ministry spokeswoman Hua Chunying said that Sarah McIver's case is different from that of two other recently detained Canadians.
Her detention came amid a dispute between both countries following the arrest of a senior Chinese telecom executive earlier this month.
Ms Hua said both countries are maintaining consular communication.
Canada's National Post newspaper reported that sources told them that Ms McIver had been working at a school in China when she was detained, apparently due to issues with her work visa.
Ms Hua said she was "serving administrative punishment due to illegal employment".
Former diplomat Michael Kovrig and businessman Michael Spavor were both taken into custody in China shortly after the arrest of Huawei chief financial officer Meng Wanzhou, at the request of the US, in Vancouver on 1 December.
Mr Kovrig and Mr Spavor are being held on accusations of harming national security. Canadian diplomats were granted consular access to both men last week.
On Wednesday, Prime Minister Justin Trudeau has said he was "very concerned" about the third detained citizen but noted Canada believed her case was different from Mr Kovrig's and Mr Spavor's.
China has denied the detention of both men is tied to Ms Meng's arrest, but many analysts believe it was a tit-for-tat action.
Beijing had threatened unspecified consequences if Ms Meng was not released.
Ms Meng has been granted bail but may face extradition to the US on charges of violating American sanctions on Iran through Huawei's business dealings. She denies the allegations.