Nicosia, Cyprus (CNN) -- Two top Cyprus officials resigned Monday after an explosion at a naval base killed at least 12 people in the island nation, state radio reported.

Defense Minister Costas Papacostas and National Guard Chief Petros Tsalikides resigned, Cyprus state radio said.

About 50 people were wounded in the blast at the Evangelos Florakis Naval Base at Zygi, the station said.

Among the dead are five firefighters and two sailors.

A grass fire spread to the base, setting dozens of crates of gunpowder on fire and causing the blast, the station said.

Greece's defense ministry announced Monday that it was sending a C-27 aircraft and military experts to help authorities with their investigation of the blast.

The explosion knocked out power at the neighboring Vasilikos Power Station, the nation's largest electricity plant, the power company said.

State radio reported that 40% of the island was without power and government officials were making arrangements for generators to be shipped into the country.

In the meantime, the nation's other two power stations were "trying to meet the demand," said Costas Gavrielides, a spokesman for the country's electricity authority.

Roads leading to the base have been blocked off, with no one allowed to enter or leave, the news agency said.

"Today is a black day for the Cypriot democracy and its people because of the loss of lives of our compatriots and injuries," said President Demetris Christofias. "I offer my condolences to the families of those who died in the line of duty."

Journalist Paul Malaos also contributed to this report.