Zanzibar's energy minister said Friday that a month-long power blackout would last six more weeks, amid mounting criticism of the government over a crippling electricity crisis.

"We expect that we shall have power on the island on February 20," Mansour Yussuf Himid said at a press conference in the semi-autonomous Tanzanian island's capital Stone Town.

The archipelago's main island, Unguja, has been without power since December 10 due to a breakdown affecting the 30-year-old undersea cable providing electricity from the mainland.

The minister assured Zanzibaris that the government was working around the clock to fix the problem and said that Tanzania's development partners were to hold an emergency meeting next week.

Opposition parties in Zanzibar, where elections are to be held later this year, have accused the authorities of mismanaging the crisis and called for the ministers in charge to resign.

The Chama cha Demokrasia na Maendeleo party had planned a mass protest in Stone Town for Sunday but the police turned down the request, arguing the demonstration would interfere with independence celebrations.

Amani Karume, Zanzibar's president, on Thursday brushed criticism aside and insisted the blackout was the result of an accident.

"At difficult times like now, media and well-wishers should sympathise with us and console us instead of pointing an accusing finger," he said at a bank inauguration.

Officials have already reported a drop in revenue collection due to the blackout and warned that the peak tourism season was also being affected.