Tanzania's electoral commission on Wednesday barred the presidential candidate of its second biggest opposition party from contesting polls in October, leaving President Samia Suluhu Hassan to face only candidates from smaller parties.

The Independent National Electoral Commission approved Hassan and her running mate, Emmanuel Nchimbi, to run in the October 29 election after receiving their nomination forms earlier on Wednesday.

The vote will be held without the participation of the leading opposition party, CHADEMA, which was disqualified in April after failing to sign the electoral code of conduct as part of its call for electoral reforms.

INEC also declined to take nomination forms from presidential candidate Luhaga Mpina of the Alliance for Change and Transparency (ACT-Wazalendo), the second largest opposition party, the party said on Wednesday.

The election commission's chairperson did not immediately respond to a request for comment after a commission spokesperson referred Reuters to him.

After her nomination was cleared, Hassan shared a post on X urging her Chama cha Mapinduzi (CCM) party to "maintain unity to ensure victory for our party and for God's permission to return to serve citizens".

CHADEMA chairman Tundu Lissu has been in jail for over four months after being charged with treason early in April. He has denied the charges.

Lissu's detention and the unexplained abductions of government critics in recent months have shone a spotlight on Hassan's human rights record. Hassan says her government is committed to respecting human rights.

On Tuesday, the Office of Registrar of Political Parties disqualified Mpina, citing complaints from a party member who said the party had failed to comply with nomination procedures in the primaries.

Mpina, a government critic and a former ruling party member of the East African country's parliament, defected from CCM earlier this month.

"This decision is not only shameful but it is raising more questions about the integrity, seriousness, professionalism and the independence of the electoral commission," Ado Shaibu, ACT-Wazalendo's Secretary General, said in a statement on Wednesday.

Hassan is running for the presidency for the first time after assuming office following the death of her predecessor, John Magufuli, in 2021.

Nominations for presidential candidates closed on Wednesday.