Voters across Russia started casting their ballots in the country's sixth parliamentary elections on Sunday, with seven political parties vying for slots in the 450-seat State Duma, the lower parliamentary chamber.

The first polling stations to open were in the Far Eastern regions of Kamchatka, Chukotka, Magadan and Sakhalin, where voting started at 8 a.m. local time on Sunday (2000 GMT Saturday).

In a vast country split by nine time zones, as voters in the western regions including the capital Moscow began to cast their ballots at 400 GMT Sunday, polling was already in full swing in Siberia and Far East.

Interior Ministry said more than 320,000 police officers and 11,500 servicemen would be deployed to maintain security during the polling.

"All polling stations in the country will be patrolled by police tasked not only with maintaining security, but also with preventing violations of the electoral law, including illegal campaigning and bribery of voters," a spokesman for the ministry said.

In North Caucasus regions, metal detectors were installed at polling stations before the vote.

Russian media said some 55 percent of the country's 110 million eligible voters are expected to cast their ballots in some 94,000 domestic polling stations and about 370 overseas stations in more than 140 foreign countries.

In Moscow, voters will go to over 3,300 polling stations, including President Dmitry Medvedev and Prime Minister Vladimir Putin.

Voters in Kaliningrad will be the last to cast ballots at 2100 Moscow time (1700 GMT) on Sunday.

First overseas polling stations to open is in New Zealand where voting started at 1900 GMT Saturday and the last ones will be in San Francisco of the United States.

The seven political parties competing in the elections are the ruling United Russia party, the main opposition the Communist Party, the Liberal Democratic Party of Russia, A Just Russia, the Yabloko (Apple), the Patriots of Russia and the Right Cause.

Some 3,000 candidates have been registered on the federal lists.

According to new electoral laws amended in late 2008, the new Duma emerging from the elections will serve a five-year term instead of four, Xinhua reported.