Power cuts which have caused havoc in Cape Town are the result of sabotage possibly intended to influence South Africa's local polls, a minister says.
President Thabo Mbeki is confident of victory
Minerals and Energy Minister Lindiwe Hendricks said there was a "curious coincidence" with Wednesday's polls.
"Clearly other forces are at play here," she told local media.
The opposition has used the power cuts to illustrate what it says is the failure of the ANC government to deliver good services.
Cape Town is one of the few parts of South Africa where the ANC does not have an overwhelming majority and could be defeated.
Public Enterprises Minister Alec Erwin also said that the damage at one of the Koeberg nuclear power plant's two generators was deliberate.
Achievements since 1994
1.8m new houses built or being built
70% households electrified
11.4m access to water
2.4m families still in shacks
3.2m houses need electricity
3.5m people without water
Source: South African government
"Let me be very clear on this. The bolt that caused the generator's destruction did not get there by accident," he said.
The generator has not been working properly since December.
President Thabo Mbeki acknowledged that the ANC had come in for "very strong criticism" during the campaign - mostly over service delivery and corruption allegations - but said he was confident of victory.
There have also been violent protests by people demanding housing and against plans to redraw provincial boundaries.
While many people in squatter camps do not have access to running water and mains electricity, such services have been delivered to millions of poor South Africans since the end of apartheid in 1994.
The largest opposition party is the Democratic Alliance but this suffers from charges that it mostly caters for the white minority.