MAPUTO, Mozambique (AP) — Mozambique's main opposition party said it found an incident of possible fraud during voting in the national election on Wednesday.

Renamo officials at a polling station in the northwestern Tete province say they prevented boxes stuffed with ballots already marked in favor of the Frelimo candidate, Filipe Nyusi, from entering a local polling station. Some Renamo officials were arrested and others reported the incident to international observers.

"We insisted that we wanted to see the ballot boxes but they refused to let us in," said Lynda Harper, a European Union observer who was at the polling station.

When voters realized what was happening, they allegedly grabbed the ballot boxes and burned them. Renamo members also claim police opened fire on the crowd but they were unsure whether they fired live ammunition, rubber bullets or tear gas.

Tete is traditionally a stronghold of the ruling Frelimo party that has been in power since 1994. Mozambique's National Elections Commission said they were investigating the incident.

Polls closed at 6 p.m. local time but electoral officials said they would allow people already in lines to vote.

More than 10 million Mozambicans are eligible to vote of the country's 26 million people. The past two elections have seen turnouts of less than 50 percent, according to the Electoral Institute of Sustainable Democracy in Africa. Mozambicans are also voting for representatives in the 250-member National Assembly.

Mozambique's election comes just months after a peace accord between the ruling Frelimo party and Renamo ended nearly two years of sporadic fighting in the north of the country. The two political parties were once guerrilla movements, fighting each other in the southeastern African nation's brutal civil war.

Earlier today Renamo leader Afonso Dhlakama called for peaceful elections. Dhlakama joined the presidential race only weeks ago, after emerging from hiding in the northern Gorongosa Mountains during the renewed violence.

These elections are the most hotly contested, according to Fernando Lima, a Mozambican journalist living in the capital Maputo. Along with Nyusi and Dhlakama, relative newcomer Daviz Simango, leader of the Mozambique Democracy Movement, is popular among young people.

"The elections will be very tight, no one can predict who will win," said Lima. "There is a possibility that this may go to second round."

Mozambique introduced a number of electoral reforms earlier this year in order to ensure a free and fair vote, including regulation of campaign advertisements on television and the distribution of a complete electoral register 50 days before the vote. Renamo has challenged the outcomes of all previous elections calling them "puppet shows."