Venezuelans have overwhelmingly approved a new constitution in a referendum at the centre of political reforms put forward by the President, Hugo Chavez.

With some two-thirds of ballots counted, more than 70% of voters had backed the changes. Over half the electorate, however, stayed away.

The new constitution could allow Mr Chavez to stay in office for up to 13 years. It also abolishes the Senate, strengthens the role of the military and reinforces state control of the country's huge oil industry.

As the results were announced, celebrations broke out on the streets of the capital, Caracas.

Venezuelans will now go to the polls within three months in presidential, parliamentary and regional elections.

Mr Chavez said before casting his ballot that the vote was a defining moment in Venezuelan history.

He had argued that the constitution was necessary to root out corruption and eliminate poverty, but his critics said it would concentrate too much power in his hands.

The BBC's Peter Greste in Caracas says that the low turnout could undermine Mr Chavez, who had staked his political future on a resounding victory.

Polls closed two hours later than initially planned because torrential rain delayed the opening of several voting stations.

'Strengthening democracy'

The new constitution is a key part of radical political reforms, which the former paratrooper promised when he came to power early this year.

Opponents of the changes say they set a dangerously authoritarian trend, which allows for excessive state meddling in the economy - a move which could scare off investors.

But the president has said the reform would strengthen democracy, improve human rights and turn Venezuela into a less corrupt country where wealth is more equally distributed.

"Venezuela is a timebomb that we have to start defusing," Mr Chavez said a few hours before voting started.

Most of his support is thought to have come from impoverished Venezuelans, who make up 80% of the population.

No quick fix

The president said the constitutional reform would usher in an economic recovery to the oil-rich, but recession-hit country in about a year.

He was confident new foreign investment, notably from Asia and the US, would start flowing into the country.

But Mr Chavez warned change would not come overnight.

"I have never promised a rose garden," he said. "Quite the opposite. I have said Venezuela would have to cross a long stretch of desert."

He estimated that within 10 years, the country's "pain should have lessened".