The power crunch in Java and Bali, which started late on Wednesday, was the result of an electricity deficit of about 1,000 megawatts. The outages are continuing into Thursday even though the power deficit has been halved, the official said.

The blackout is likely to spread to other areas in Java if coal supplies do not pick up soon, said Mulyo Adji, PT Perusahaan Listrik Negara's (PLN) spokesman.

'Some power plants are running below capacity and some of them are going back to fuel oil. We have turned off supplies to severals areas in Java as PLN has a power deficit,' he said.

'Coal supplies to some power plants in Java have been stopped as ships cannot go to ports because of big waves.'

Power demand in Indonesia has been soaring due to its brisk economic growth, forcing Asia-Pacific's only OPEC member to tap other sources of energy such as coal and natural gas in the face of rising crude oil prices and dwindling domestic reserves.

PLN has a monopoly over power supply in Indonesia and has 24,000 MW of generating capacity, but daily output is far below capacity because most its plants are ageing. Some 30 per cent of the plants use oil products such as diesel and fuel oil.

Mr Adji said the Tanjung Jati power plant in central Java, which has a capacity of 1,200 MW, was operating on 250 MW. Some other power plants were also operating below capacity.

Indonesia plans to step up power generation capacity to meet soaring demand by building new coal-fired and natural gas plants, but the projects need huge investments. Officials say domestic electricity demand is growing at around 10 per cent a year.

Indonesia's power sector has been beset by problems because of ageing plants, high costs and low funds as tariffs are highly subsidised and still among the lowest in the world.

Indonesia has not increased electricity tariffs for several years because of opposition from parliament. The government wants to add 24,000 MW of electricity by 2013 from projects estimated to cost US$30 billion (S$42 billion).

This includes a plan to generate an additional 10,000 megawatts (MW) using coal as a source by 2010.

Indonesia domestic coal consumption was estimated at 49 million tonnes in 2007, with domestic power plants accounting for 74 per cent, or 36.4 million tonnes.

The government estimated coal output was 196 million tonnes in 2007, while industry estimates pegged the figure at 215 million tonnes. -- REUTERS