Shops in the capital Caracas have been dimming their lights to conserve power
Venezuela has announced an electricity rationing programme in which the entire country will be affected by four-hour blackouts every week.
The government said cuts would be made in different blocs around the country every other day, adding to blackouts which regularly affect the south.
The opposition accuse the government of failing to invest in infrastructure.
But ministers say the problem has been caused by a water shortage which is affecting hydro-electric production.
The BBC's Will Grant in Venezuela says it has not been the easiest year so far for the government of President Hugo Chavez.
Having already announced a currency devaluation, the government has now had to tell the Venezuelan people that they can expect regular blackouts nationwide, our correspondent says.
Electricity Minister Angel Rodriguez told state television that the cuts were the result of critically low levels of water at the country's main hydro-electric dam.
"With these measures, we're trying to keep Guri from taking us to a very critical situation at the end of February, from creating, let's say, a total shutdown of the country," he said.
The Guri dam meets around 70% of the country's domestic energy needs.
Many customers in Venezuela are angry that one of the world's largest oil producers will be suffering such blackouts, but this is a situation which has been coming for several months, our correspondent notes.
The interior of the country has been experiencing electricity cuts for some time, and recently Mr Chavez advised people to spend no more than three minutes in the shower to conserve water and electricity.
State television now features regular advice on how to brush your teeth without wasting water and reminders to switch off air conditioning and lights.