The price of water has doubled on the island
Businesses in Zanzibar are closing down and residents are bemused as a power cut affecting the whole of the Tanzanian island enters its eighth day.
The BBC's Frederica Boswell in Zanzibar says there has been little official information about the blackout.
It began after a massive power failure in Tanzania; power was restored quickly on the mainland, but not in Zanzibar.
There are concerns that without running water, usually pumped into homes, there could be an outbreak of cholera.
It is Zanzibar's worst power crisis for years, our correspondent says.
Generators have sold out and the price of water has doubled - a 20-litre container of water now costs $1 (50 pence).
There is confusion about the cause of the failures, our reporter says.
Tanzania's state electricity company blames a blown transformer, although some media reports suggest it was a submarine cable that was affected.
Many cafes in Stone Town have closed down.
One cafe owner told the BBC she could not afford to spend $100 (£50) a day on fuel for a generator.
The cost of running a generator for one day is the equivalent to half a month's electricity bill, some residents say.
People are desperately looking for places with generators to charge their mobile phones, our reporter says.
There are also concerns that the power cut could affect the island's crucial tourist industry.
The Africa House Hotel says it is spending 20% of its daily revenue on diesel and water for its residents.