The South African National Editors' Forum (Sanef) said it was disturbed to learn of the brief detention of Committee to Protect Journalist's Angela Quintal and Muthoki Mumo.
South Africa's Department of International Relations and Cooperation (Dirco) said the two journalists are back in their hotel.
South Africa's High Commissioner Thami Mseleku is meeting with the pair to discuss the details of their arrest.
"If they want to engage themselves in anything more than a normal visit then they have to request appropriate permits", spokesperson for Tanzania's immigration ministry Ally Mtanda is quoted to have said.
Quintal tweeted before 1am on Tuesday morning that she and her colleague had been released, but Quintal's family raised concerns that the tweet did not sound as if it had come from Quintal whose Twitter account was subsequently suspended. Quintal and Mumo's passports were confiscated and were yet to be returned.
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Louis gained renewed interest past year when picture and stories of the victims circulated on social media in response to U.S. President Donald Trump's decision to ban immigration and refugee settlement from certain countries.
Quintal is a respected South African journalist and former editor of the Mail and Guardian newspaper‚ now working for the media freedom group based in America. We don't know why.
Their communication devices were also taken away and used to relay falsified information. We need to urgently find out the reasons behind this detention.
The Committee to Protect Journalists (CPJ), through its Twitter account, called on the Tanzanian authorities to immediately release the two members of the committee and return their passports.
Angela Quintal and Muthoki Mumo were permitted to return to their hotel in Dar es Salaam after being taken to an unknown location and subjected to "several hours of questioning", according to a news release.