Nine Tanzanian government ministers have lost their parliamentary seats to the opposition Ukawa coalition, partial results from Sunday’s vote show.
It is the biggest shock of the election so far which is the most competitive in the country’s history.
The BBC’s Arnold Kayanda in the main city Dar es Salaam says it is a big blow to the governing CCM party.
But it is too early to predict the end of its 54-year rule as there are many results still to be declared, he says.
The electoral commission has until Thursday to announce the final results.
Agriculture Minister Stephen Wasira – a veteran CCM politician of over three decades – is among the high-profile ministers who lost their seats in Sunday’s election.
Others include Investment Minister Christopher Chiza, Deputy Health Minister Stephen Kebwe and Deputy Education Minister Anna Kilango Malecela.
Observers from the European Union have given a positive assessment of the polls.
But they raised several concerns – including the apparent failure of state media to give fair and equitable coverage to the opposition in the build-up to the election.
Zanzibar electoral commission lockdown
On the semi-autonomous archipelago of Zanzibar, the announcement of the election was temporarily suspended after soldiers stormed the collation centre, eventually evicting journalists and observers.
The opposition Ukawa coalition on Zanzibar had already expressed concerns about the results announced so far.
Residents on the islands also voted for their own president and members of the Zanzibar parliament on Sunday.
About 70 armed soldiers invaded the compound of the electoral commission and locked journalists, local and international observers inside the main hall.
Officials also stopped announcing results.
The soldiers ordered all of us to stay where we were and when I tried to ask them why, they told me not to approach them or question them.
After more than three hours, they allowed us to leave the electoral commission premises and told us not to come back until further notice.
Electoral officials reconvened and decided to postpone any further announcements until Wednesday.
CUF, one of four parties which make up Ukawa, accused the Zanzibar electoral commission of only releasing results from constituencies where the CMM candidate won.
On Monday, Ukawa candidate Seif Sharif Hamad declared himself the winner of the Zanzibari presidential poll.
Correspondents say tension has been rising on the islands ahead of the final results.
Previous elections have turned violent on Zanzibar, which is made up of the islands of Unguja and Pemba and is a popular with tourists.