Some reports say the death toll could be high as 40 but officials have not confirmed this.
Tens of thousands of people had turned up at a stadium in Dar es Salaam to view the body of the former president.
Nicknamed the bulldozer, Mr Magufuli was popular with many Tanzanians for his no-nonsense governance style.
Critics, however, accused him of being an autocrat and of clamping down on dissent.
He also downplayed the effects of coronavirus and stopped the publication of the country's case numbers and deaths. Opposition politicians say that Mr Magufuli died from Covid-19, but this has not been confirmed.
Dennis Mtuwa's wife, two of his children, a nephew and a niece have been confirmed among the dead after Sunday's stampede, reports the BBC's Salim Kikeke from Dar es Salaaam.
"These last 24 hours have been really difficult for me. I feel relieved when I'm surrounded by people, but when I'm alone the amount of grief becomes overwhelming," Mr Mtuwa told the BBC.
The city's Police Commander Lazaro Mambosasa said he would give further details on Tuesday.