Quintal works as CPJ's Africa program coordinator while Mumo is CPJ's sub-Saharan Africa representative.
The International Relations Department says they have since been released, but details of exactly what transpired are still unclear.
After "a very long night"‚ the department of worldwide relations and co-operation on Thursday confirmed that South African journalist Angela Quintal and colleague Muthoki Mumo had been released after being detained by authorities in Tanzania.
Quintal is Africa programme co-ordinator at the Committee to Protect Journalists (CPJ), and Muthoki Mumo is CPJ's sub-Saharan Africa representative.More news: Fantastic freshmen help No. 4 Duke blow out No. 2 Kentucky
Quintal sent a message Wednesday from her verified Twitter account saying she and her colleague were "being taken for interrogation by Tanzanian authorities and we don't know why?"
"He will then proceed to engage the Tanzania authority. The high commissioner, [Thami] Mseleku, is meeting with them to understand the events of last night‚" department spokesperson Ndivhuwo Mabaya said. We need to urgently find out the reasons behind this detention.
The Tanzanian government spokesman however said that they were arrested because they wanted to establish how the two entered the country. "We believe the arbitrary detention of journalists is a direct and unsafe threat to media freedom and access to information".
"Quintal and Mumo were then escorted from the hotel and have been taken to an unknown location‚" said the CPJ. "We are concerned for the safety of our colleagues Angela Quintal and Muthoki Mumo, who were detained while legally visiting Tanzania". They were released on Thursday morning but are yet to get their passports back.