Cambodia's political parties have officially started campaigning for next month's general election, which is expected to extend the rule of Prime Minister Hun Sen, Asia's longest-serving leader.

Hun Sen's Cambodian People's Party (CPP) is expected to win the July 28 polls in a landslide.

Hun Sen has run Cambodia since 1985 with little tolerance for opposition.

Eight parties are taking part in next month's polls to elect 123 lawmakers to the lower house of parliament. The winner forms a new government to run Cambodia for the next five years.

The main opposition party's leader, Sam Rainsy, is in self-imposed exile in France to avoid 12 years in prison for convictions widely seen as politically motivated.

Hun Sen and other CPP leaders marked the start of campaigning on Thursday by receiving a blessing from the country's top Buddhist monks in front of tens of thousands of supporters.

"Making a right decision will bring more success, but a wrong decision will be a setback and a huge danger for the nation," Heng Samrin, the CPP honorary president, told the rally.

Thousands of supporters from several political parties took to Phnom Penh's streets in colourful rival rallies, as cars and motorcycles adorned with political banners roared through the capital.

Some 9.6 million people are registered to vote under the eyes of more than 7,700 domestic and international observers.

Source: Agencies