Zanzibar presidential candidate on the ruling CCM, Aman Abeid Karume, casts his vote at Kiembe Samaki poling centre in Zanzibar

Zanzibaris went the polls in elections some voters say were riddled with irregularities. News reports say Police and ruling party militia clashed with opposition supporters in the streets of Zanzibar's main town as voters chose between the socialists who have ruled the semi-autonomous state for three decades and an opposition promising wide-ranging reform.

Tensions were high as Zanzibaris across Unguja Island cast their ballots. Police presence was heavy at some polling stations.

Some voters allege the ruling-party Chama Cha Mapinduzi, the CCM, sent groups of supporters from polling station to polling station, voting for the party.

At Forodhani station in Stone Town, a voter who gives his name as Ali describes to VOA the situation there.

"There are some people who are not supposed to vote in this place, but they are coming here to vote," he said. "And we know; all people who live here, we know. The people tried to tell them, you are not supposed to come here, and they chased them away. There are those people who have two voting cards and have come here. I do not know if that is democracy."

International news reports say soldiers fired into the air during a clash in Stone Town with opposition supporters angry about the arrival of government supporters in vehicles shepherded by the military.

At a nearby secondary school, voter Salim Mohamed Abdallah says he recognized plainclothes police officers from outside the polling station area who he says were sent to vote for the ruling party.

"They come to vote in this station, and they have no right to vote here," noted Mr. Abdallah. "So we are very, very worried about that. I am sure they are going to vote in more than one, two or three stations."

Meanwhile, opposition presidential candidate Seif Sharif Hamad said several of his party officials were seized by police in the early hours and are being held. Assistant Police Commissioner Khamis Mohammed Simba tells VOA security agents caught the officials carrying boxes that looked like ballot boxes, and that police are investigating the incident.

Other irregularities voters reported to VOA include not being allowed to cast a ballot despite their names appearing on a voter's list; the voter ID numbers on their cards not matching those on the list; and being harassed by security forces.

Six presidential candidates are running, but the key contest is between the ruling party and the main opposition party Civic United Front, known as CUF.

The Civic United Front has repeatedly accused the ruling party of fomenting violence, using state resources to ensure their victory in elections, blocking more than 12-thousand voters from registering, and training young people to attack opposition supporters with crude weapons.

The ruling party denies these allegations and says it is the Civic United Front that is causing violence and making up stories because it knows it will lose the elections. Police insist they are not using heavy-handed tactics to intimidate voters, and deny manipulating the electoral process to ensure a CCM victory.

Mohammed Bilal, a ruling-party official observing the elections, tells VOA that, of the polls he has seen so far, in his words, everything is going well, and that people are calm.

Mr. Bilal says he has not heard reports that CCM is ferrying in people to vote at different stations. He tells VOA that if CCM or other parties transported voters to stations, it was because the voters were unable to get there themselves.

"What I know is that some people who are not well, who are sick or possibly incapacitated in one way or another, they will be helped by the parties or something like that," he added. "Sometimes these polling stations have people who are from very far, they are much bigger, they are much more spread out, and possibly people will be helping others, maybe those who could not on their own walk from some distances to this place."

Some locations were quiet and orderly. At the Jang'ombe polling station on the outskirts of Stone Town, voter Saleh Mahmud Jabir tells VOA he believes the elections are being conducted in what he calls a free and fair manner.

Mr. Jabir says everything is OK. It seems it is quiet, he says, nothing bad has been happening and he is very happy.

Election observers watching the Zanzibar polls are expected to issue statements on their findings during the next few days.