Looting and violence have been reported in parts of Venezuela, as the country faces widespread food and power shortages, forcing the government to ration food and electricity.

Several towns and cities, including the second-biggest city Maracaibo, were hit by rioting on Tuesday and Wednesday after daily power cuts started from Monday.

"The situation is critical," said Norvelis Contreras, a 26-year-old housewife, who had been queueing for five hours to buy rice and oil on Thursday at a supermarket in Maracaibo.

"We are suffering and trying to survive," she told AFP news agency.

Residents in the Caracas area of Petare this month said they were eating more starches and skipping meals because they could not find food or afford to buy what was available.

"I have to leave the house at 5am, facing the risk of being killed, to stand in line all day and only buy two or three products," Jhonny Mendez told the Reuters news agency.

In a survey published by pollster Venebarometro on Thursday, 13 percent of Venezuelans said their household only ate once a day.

Another Venebarometro poll indicated more than two thirds of Venezuelans wanted President Nicolas Maduro to quit.

The opposition blames government mismanagement for the power crisis as well as for the shortage of food and basic supplies.

The opposition tried to sack the food minister, but it was blocked by President Maduro.

"We are facing the worst food emergency in Venezuela's history," said Ismael Garcia, an MP leading the motion to sack Food Minister Rodolfo Marco Torres.

The socialist president has already blocked several bills brought by the opposition by challenging them in the Supreme Court. His critics say he controls the court and the electoral authorities.

'Economic war'

On Thursday, the opposition, which took control of the legislature in January, said that a million people backed its call for a referendum to remove the president.

The signatures will be handed over to the National Electoral Board, which will take a final call on whether the referendum can be organised.

Maduro blames the situation on an "economic war" against the country by capitalists and right-wing conspirators seeking to destabilise his government. He has vowed to press on with the socialist "revolution" launched by his late predecessor Hugo Chavez in 1999.

He also says the El Nino weather phenomenon has dried up the country's hydroelectric dams.

To save power, his government has also slashed the working week to two days for state employees and ordered schools to close on Fridays.

Since Maduro became president in 2013 after Chavez died of cancer, the economy has been hit with shortages and skyrocketing inflation.

The collapse of global crude prices have worsened the economy of the Latin American nation with the world's largest oil reserves.

The political tension, shortages and now enforced electricity blackouts that started this week have raised fears of unrest in the country, already ranked by the United Nations as one of the most violent in the world.