The officials searched the pair's belongings and would not return their passports when asked, according to Quintal.
CPJ believes that their colleagues' electronics might have been compromised since a tweet was sent from Quintal's account stating that they had been released but no one has contacted them directly from the organisation.
Mr Simon urged the Tanzanian authorities "to halt their ongoing crackdown against a free press".
The two were on a reporting mission for the Committee to Protect Journalists.
Tanzanian immigration authorities detained Committee to Protect Journalists Sub-Saharan Africa Representative Muthoki Mumo (left), and Africa Programme Coordinator Angela Quintal in Dar es Salaam on November 7.
"Immigration spokesperson Ally Mtanda told The Citizen that the department had arrested the two journalists and questioned them, saying, "...they arrived in the country on October 31, 2018 through the Julius Nyerere International Airport (JNIA) in Dar es Salaam and they said the objective of their trip was normal visit".
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Quintal is a respected journalist and former editor of the Mail & Guardian newspaper‚ amongst other senior positions‚ now working for the media freedom group based in America.
Simon commended the attention brought to the case by "journalists, media and press freedom organizations, and government officials", and noted that the South African and Kenyan governments were of particular assistance.
There is confusion around whether or not well-known South African journalist Angela Quintal and her colleague have been released after appealing for help on social media, saying they had been taken for interrogation in Dar es Salaam, Tanzania.
He added that both women were now at the South African embassy in Tanzania's economic capital Dar-es-Salaam. "Quintal and Mumo were then escorted from the hotel and. taken to an unknown location".
"Angela Quintal and Muthoki Mumo travelled to Tanzania to understand the challenges facing the Tanzanian press and to inform the global public", the CPJ boss said.
Soon after their detention, an uncharacteristic tweet was sent from Quintal's Twitter account - reading "God is great we are released going back to our hotel" - raising fears that someone had accessed her electronic devices. Both of their Twitter accounts remained suspended at the time of publication.