Zanzibar Electoral Commission chairman, Jecha Salim Jecha said in a statement, "I hereby officially announce that this election and all its results have been annulled and there is a need to hold fresh elections."
The election in Tanzania's semi-autonomous region of Zanzibar has been annulled due to abuses, the regional electoral commission said and called for a new election to be held on the island.
Zanzibaris voted in local and national elections last Sunday, criticisms has been focused largely on the vote in the Pemba Island.
Coalition of four opposition parties called Ukawa and their candidate Seif Sharif Hamad, announced that they were the winner of the Zanzibari presidential election.
Governing party officials said the declaration was illegal and risked the islands' stability.
According to official results announced by the National Election Commission (NEC) on late Tuesday, candidate John Magufuli of the long-governing Chama Cha Mapinduzi (CCM) party won 56.51 percent of the vote, while his main rival Edward Lowassa of the opposition Chadema party had 41.67 percent.
After opposition challenger Seif Sharif Hamad of the Civic United Front (CUF) repeated concerns that he "will not concede defeat if robbed of my victory," security forces surrounded the election result centre of the island on Tuesday.
Although security forces left the centre, according to an AFP reporter, shots rang out at night and the streets were empty, many shops were closed on Wednesday, because people were afraid to go out.
International observers generally praised the election on Sunday.
African Union Commission chief, Nkosazana Dlamini-Zuma has praised Tanzania for the carrying out of the elections, but also warned the candidates to "think of their country above all other interests."