Venezuela's government has imposed rolling blackouts of up to four hours every other day throughout the country to help combat an energy crisis.

Hugo Chavez, the president, has said rationing is necessary to prevent water levels in the country's main dam from falling to critical lows and causing a widespread power collapse.

The blackouts will begin on Wednesday in the capital, Caracas.

"This plan is going to be implemented throughout the country,'' Angel Rodriguez, the electricity minister, said.

"In some places, it will be four hours, in others it will be three hours."

The increased rationing will help cover a 12 per cent gap between energy supply and demand, due to the situation at Guri Dam and at some thermoelectric plants that are operating below capacity, Javier Alvarado, president of the city's state electric utility, said.

Drought reduced the flow of water into the Guri, which feeds three hydroelectric plants that supply 73 per cent of Venezuela's electricity, he said.

Reduced supply

Government officials had already imposed some cuts to help the country get through the dry season until May, when seasonal rains are predicted to return.

The government recently reduced the hours of electricity supply for shopping centres and required businesses and large residential complexes to cut energy use by 20 per cent or face fines.

Chavez announced last week that many public employees will have shorter workdays from 8am to 1pm, except those in offices that tend to the public.

Alvarado said the Caracas subway, hospitals, media outlets and public institutions that tend to the public would not be affected.

Chavez's government has also partially shut down state-run steel and aluminum plants.

"With these measures, we're trying to keep Guri ... from creating let's say a total
shutdown of the country," Rodriguez said.

He said water levels at the dam in southeastern Venezuela have dropped drastically as a result of the El Nino weather phenomenon in the Pacific Ocean.

"It's a global phenomenon and it's affected us in recent months."

Chavez's critics say his government is to blame because it has failed to complete enough power upgrades to keep up with increasing demand, despite Venezuela's bountiful oil earnings.