President Amani Abeid Karume took an oath of office on Wednesday at the House of Representatives of this semi-autonomous Indian Ocean archipelago, inspected a guard of honour and took a 21-gun salute as anti-riot police, supporters and the merely curious stood outside.
With general foreign endorsement of Sunday's turbulent poll, the Civic United Front (CUF) opposition faces an uphill battle to annul the results, analysts said.
"They have been isolated by the fact that the international community said it was relatively free and fair," Tanzanian professor Ted Maliyamkono told Reuters.
In three days of clashes between security forces and opposition supporters since Sunday's turbulent poll, at least one person has died, aid groups and police said, but others put the toll higher.
Seif Shariff Hamad of the main opposition Civic United Front said five supporters died on the Zanzibar archipelago's second island, Pemba, on Tuesday, The Associated Press reported. A member of the government security force said four of his colleagues were killed on Pemba. He spoke on condition of anonymity because he was not authorized to talk to the media.
Scores of others have been injured and arrested.
The opposition says it was again cheated in its third successive electoral effort to wrest power from the ruling Chama Cha Mapinduzi (CCM or Party of the Revolution), which has ruled in Zanzibar and across Tanzania for four decades.
Civic United Front supporters help
injured comrades in the capital
But the government accuses the opposition of trying to bring chaos to the tourist islands of 1 million, and says its candidate, incumbent President Amani Abeid Karume, won fairly.
Karume, son of Zanzibar's first post-independence leader, was to be reinaugurated at 9am (0600 GMT).
Privately, many foreign election observers have expressed misgivings over the violence and noted numerous irregularities including multiple voting, incomplete voters' registers, and intimidation by security forces.
But in their public assessments, the Southern African Development Community, the African Union and the Commonwealth have all given a thumbs-up overall to the election.
"Overall, this was a good election," the Commonwealth said.
The US-based National Democratic Institute issued a harder-hitting report, condemning "excessive use of force" and irregularities but concluded that the election was a "marked administrative improvement" on past Zanzibar polls.
The government's victory, by 53.2% of votes to 46.1% for the opposition, was a relief for Tanzanian President Benjamin Mkapa, whose only real political threat is on Zanzibar, traditional stronghold of the opposition CUF.
Security forces and protesters
have clashed for three days
"Mkapa and the CCM are going to be relieved that the results are endorsed but nervous about whether the results will trigger more of the violence we saw in 2000," UK-based Africa expert Tom Cargill tpld Reuters.
Mkapa is popular with the international donor community and was a member of British Prime Minister Tony Blair's prestigious Commission for Africa that drew up recommendations for changes on the continent for the G8 rich nation group.
Reputation for stability
Mkapa stands down at a national election on 18 December, and his party's candidate, Foreign Minister Jakaya Kikwete, is on course to win easily, analysts say.
Tanzania enjoys a reputation as one of Africa's most stable nations, but troubles in Zanzibar, 40km (25 miles) off the coast in the Indian Ocean, have sullied that.
After the government won a 2000 election on the mainly Muslim islands, 35 opposition protesters died and several thousand fled to Kenya.
The opposition said on Tuesday that it had reports five of its members were killed on Pemba, the smaller of Zanzibar's main two islands. Aid groups and police confirmed one death in the village of Wete, but said they had not verified any more.
Dressed in green-and-yellow party colours, government supporters danced, waved flags and celebrated late into the night after Tuesday's announcement of victory. "God is great, we will now have peace," said Mohamed Saidi Mohamed.
The ruling party, which has socialist roots, says it is the guarantor of stability on Zanzibar. The opposition had promised democratic reforms and privatisation, including of the clove industry which is the second revenue-earner after tourism.
Dismissing the victory as "doctored", opposition leaders said they would organise peaceful demonstrations. "Once again the democratisation process in Tanzania has failed in Zanzibar," CUF national president Ibrahim Lipumba told Reuters.
For a third day on Tuesday, police fired dozens of tear gas rounds to disperse groups of opposition supporters gathered in the narrow alleys near their party headquarters in the capital, Stone Town.
The government has held Zanzibar since the 1964 toppling of Arab rule. It allowed a multiparty system in Tanzania in 1992.