He was due at a science conference on Wednesday in Arusha but was instead represented by a cabinet minister.
His disappearance from public view has sparked rumours about his health.
But Prime Minister Kassim Majaliwa has warned against such speculation, saying the vice-president was out of the country for official duties.
This is not the first time there have been rumours about the state of the vice-president’s health.
Before becoming vice-president, Mr Mpango, 66, had served as finance minister under the previous President, John Magufuli, who died in office in March 2021.
A month earlier, during the COVID-19 pandemic, Mr Mpango appeared at a news conference in the capital, Dodoma, to deny a rumour that he, himself, had died. He coughed several times as he paid tribute to senior government officials who had passed away.
Under the country’s constitution, if the president dies, resigns, is permanently incapacitated or is disqualified, the vice-president takes up the presidency for the rest of the term.
Mpango was lastly seen in public on 31 October while representing President Samia Suluhu Hassan during a virtual meeting of leaders from the Southern African Development Community.
On Monday, the president had to cut her trip short in Dubai to deal with deadly landslides in the northern region.
Some social media users have been expressing concerns about the uncharacteristic silence of Mr Mpango, who is yet to comment about the tragedy in Hanang region.
Others say they are worried about Mr Mpango’s health.
Prime Minister Majaliwa, however, said citizens should not be speculating about the vice-president’s whereabouts.
“Ignore the crazy things on social media, Dr Philip Mpango is out of the country on official duties,” Mr Majaliwa said on Saturday.
Mpango’s office did not immediately comment on the matter.
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