Caracas (AFP) - Venezuela's opposition presented reams of signatures to election authorities calling for a referendum to remove President Nicolas Maduro, who they say is to blame for a crushing economic crisis.

Venezuelans fed up with food shortages, soaring inflation and now a paralyzing electricity crunch have flocked to sign a petition for a recall referendum, according to the opposition Democratic Unity Roundtable (MUD).

It said it had presented 1.85 million signatures -- more than nine times the number needed to launch the referendum process -- to the National Electoral Board.

MUD executive secretary Jesus Torrealba said 80 boxes packed with referendum petitions had been delivered to the board.

"This is just the beginning of a road that will end in a recall referendum and the election of a unity government," he wrote on Twitter.

Maduro has vowed to see off attempts to drive him from office.

"We are not afraid of them," said Maduro's most powerful ally, lawmaker Diosdado Cabello on Monday.

"We are going to check the signatures one by one."

- Bias claims -

Maduro's opponents are racing to hold a recall referendum before the end of the year.

Under Venezuela's constitution, after January 2017 a successful recall vote would transfer power to Maduro's vice president rather than trigger new elections.

The constitution gives the authorities five days to count the signatures collected by the opposition and five days to verify them.

But electoral board official Tania D'Amelio suggested Sunday that process would begin only once the full 30 days allotted for circulating the petition had lapsed -- in late May.

The opposition accused her of bias in favor of Maduro.

It said there is no need to wait because it had already gathered more than the required 200,000 signatures "in record time."

If the electoral board accepts the signatures as valid -- far from a sure bet -- the opposition will then have to collect four million more for the board to organize the vote.

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"We'll achieve that in record time, too," said Torrealba.

Opposition leader Henrique Capriles, MUD's presidential candidate in 2013, said: "The referendum is ours, and it's the way to achieve the political change the country needs to escape this situation."

- Beer dispute -

Maduro's government has taken a series of drastic measures to deal with the electricity crisis: four-hour daily blackouts across most of the country, a two-day public-sector workweek and school closures on Fridays.

The power cuts sparked riots and looting last week in Venezuela's second-largest city, Maracaibo.

On Sunday, the country also set its clocks forward half an hour to curb evening electricity demand.

The country's biggest beermaker, Polar, stopped production at four breweries Saturday, saying it had run out of barley.

Maduro on Sunday ordered the state takeover of any companies that halt production over what he insists are trumped-up shortages invented by wealthy elites plotting against him.

Inspectors visited two Polar breweries and several distribution centers Monday, escorted by soldiers, a source at the company told AFP.

Once-booming Venezuela, which has the world's largest proven oil reserves, has plunged into economic chaos as global crude prices have collapsed.

The import-dependent country faces acute shortages of food and basic goods like toilet paper due to a lack of foreign currency.

The economy has been in recession since 2013 and shrank 5.7 percent last year. The government said inflation came in at more than 180 percent in 2015.

Analysts estimate the actual inflation rate is much higher. The International Monetary Fund forecasts it will hit 700 percent this year.

Maduro was elected president by a razor-thin margin in 2013. A recent poll found that more than two thirds of Venezuelans want him to leave office.