Opposition parties place the blame on the government, recalling that since Magufuli's election, their meetings have been banned, top officials arrested while newspapers have been shut and their journalists arrested or threatened for criticising authorities.
Magufuli, whose nickname "tingatinga" means "bulldozer" in Swahili, swept to power in 2015, presenting himself as a no-nonsense, corruption-busting, man-of-the-people.
But rights watchdogs say a climate of fear has set in since his election.
Some turn up dead or injured. Others are never heard of again: A wave of kidnappings in Tanzania that appears to target critics of the government has set the nation on edge.
In May, high-profile dissident Mdude Nyagali was snatched by four gunmen after leaving work, and was dumped, seriously beaten, in a village two days later, according to the main opposition Chadema party.
The incident came just hours after he had branded President John Magufuli a "hypocrite" in a Twitter post. He later blamed security forces for his kidnapping.
Nyagali was one of the lucky ones.
In February 2018 Chadema member Daniel John was kidnapped in the middle of a political campaign, only to turn up dead with machete wounds to the head.
Two years earlier, Ben Saanane, an assistant to Chadema leader Freeman Mbowe, disappeared and his fate is still unknown.
"I cannot recall a wave of kidnappings of this magnitude before 2016," said Aidan Eyakuze, a civil society activist who has written op-eds criticising a clampdown on Tanzanian media and Magufuli's approach to democracy.
The Tanzania Human Rights Defenders Coalition (THRDC) counts 17 kidnappings since 2016 of "human rights defenders, journalists, businessmen, politicians and artists".
"People say they are afraid because no one seems to be safe. In public transport and bars, people no longer talk politics. They are scared of the people seated next to them," an Arusha bus driver said on condition of anonymity.
Magufuli, whose nickname "tingatinga" means "bulldozer" in Swahili, swept to power in 2015, presenting himself as a no-nonsense, corruption-busting, man-of-the-people.
However rights watchdogs say a climate of fear has set in since his election.
"Kidnappings have increased, mainly targeting people who openly criticise the regime, in particular political opponents," said Fatma Karume, former president of the Tanganyika Law Society.
"Even amongst us, in the CCM (ruling party), people are afraid. No lawmaker dares to say anything out of fear of being targeted or struck off the list of candidates in the next election," an MP from the party said on condition of anonymity.
Opposition parties place the blame on the government, recalling that since Magufuli's election, their meetings have been banned, top officials arrested while newspapers have been shut and their journalists arrested or threatened for criticising authorities.
Opposition lawmaker Tundu Lissu has blamed authorities for an attack in 2017 which saw him shot multiple times at his home.
"The regime is behind all this. These are the tactics of a regime which does not accept any criticism," said lawmaker Halima Mdee, leader of Chadema's women's branch.
A Tanzanian journalist, speaking on condition of anonymity, said those who survive their kidnappings often remain mum on the details out of "fear of retaliation".
Opposition members and rights activists say that investigations into the kidnappings go nowhere.
As for the government, it says many of the disappearances are faked.
"On social media there are people fabricating kidnappings and disappearances. This can divide the nation and sow panic among the population," Interior Minister Kangi Lugola said earlier this month at a public gathering.
He ordered police to "find and arrest those spreading these lies in order to turn the population against the government".
In March last year, student activist Abdul Nondo was kidnapped and found injured. But when he reported the incident to police he was arrested for making it up.
A court acquitted him in November 2018.
The THRDC this month called for a "national conference" to discuss the issue of kidnappings.
