Cambodians have voted in elections expected to stretch further Prime Minister Hun Sen's 28-year rule amid alleged poll irregularities and the exclusion of the opposition chief.

The voting finished at 3pm (08:00 GMT) on Sunday, with early results expected later in the day.

The run-up to the vote has seen the prime minister appearing so confident of victory of his ruling Cambodian People's Party (CPP) that he did not even personally campaign for the parliamentary election.

As polling was still going on, the opposition Cambodia National Rescue Party (CNRP) alleged widespread irregularities, describing the problems as the worst so far.

"The situation is more serious than at any previous election," the party spokesman, Yim Sovann, told the AFP news agency.

Cambodia's opposition leader Sam Rainsy virtually acknowledged on Saturday that his party would lose the general election, saying the polls were unfair but pledging that his “fight for real democracy” would go on.

The CNRP leader told reporters that any gains his party made against longtime Sen's CPP would be significant, “and would set the stage for a long fight for fair elections”.

'Worthless' victory

Rainsy recently returned from a self-imposed exile after receiving a surprise royal pardon for criminal convictions which he contends were politically motivated.

The ruling party is nervous. That's why they block me by all means. Sam Rainsy, opposition leader

But he is barred from running as a candidate since the authorities said it was too late to add his name to the electoral register.

His party said the result would be meaningless without Rainsy's participation.

“If the prime minister wants to keep his position he must be brave enough to confront me," Rainsy told reporters on the eve of the vote.

“It's very unfair and shows that the current prime minister is really a coward... The ruling party is nervous. That's why they block me by all means," Rainsy said, adding, “Any victory under such circumstances is worthless.”

His party said it had uncovered irregularities such as tens of thousands of duplicated voter names that would allow some people to cast ballots twice.

Process 'manipulated'

Even the local poll monitor the Committee for Free and Fair Elections in Cambodia alleged that up to 1.25 million people who are eligible to cast ballots are not on the voter lists.

Meanwhile, the Cambodia Daily reported that violence broke out on Sunday at a ballot station inside the grounds of a pagoda in Phnom Penh as voters complained they could not find their names on the National Election Committee’s voter list.

New York-based Human Rights Watch has said the vote will be anything but free and fair, highlighting alleged manipulation of voter rolls and campaigning by senior security forces officers for the ruling party.

“The process has been manipulated to ensure victory for the ruling party,” said HRW Asia director Brad Adams.

While the government denies the allegations, ruling party spokesman Khieu Kanharith told AFP that the party was confident of another landslide.

“We expect to keep an absolute majority,” he said.

Hun Sen is running on a record of having restored peace and stability after decades of war and unrest, and promoting economic growth.

The opposition decries corruption and injustice, especially reflected in widespread land-grabbing that see influential companies and business people develop property from which thousands of people have been evicted.

Although Hun Sen has garnered more power, the election campaign has not been marked by the kind of violence, including killings that plagued past polls.

About 9.6 million people were registered to vote - more than one third of whom are below the age of 30.