Seven fishermen were killed as their boat was sunk by powerful winds in a rare hurricane strike off Guinea-Bissau at the start of the week, local officials said Friday.

Named Fred, the storm packed winds of up to 140 kilometres (85 miles) per hour as it hit west African waters.

A spokesman from FISCAP, Guinea-Bissau's privatised maritime control service, said the men -- from Guinea-Bissau, Senegal, Sierra Leone and Cape Verde -- had been missing since the Greek-registered Dimitrios was struck on Sunday.

"The Dimitrios was in Guinea-Bissau's exclusive economic zone when it was surprised by a storm with strong waves of up to seven metres (23 feet)," added Carlos Silva, director of the National Maritime and Ports Institute.

"The captain of the boat attempted a manoeuvre to withstand the waves but they were too strong and the ship went deep into the abyss. The ship had 19 sailors on board. Twelve were rescued by speedboat, seven others have not been found."

He said air searches launched from Senegal had also proved fruitless.

Fred was a category one hurricane on the five-point Saffir-Simpson scale as it bore down on Cape Verde at its peak on Monday, before heading northwest and weakening to a tropical storm.

It was the first hurricane to strike Cape Verde, a group of 10 volcanic islands located 500 kilometres off Senegal, since 1892, US weather experts have said.

Fred was the second hurricane of the Atlantic season.

Earlier in August, Hurricane Danny caused a tropical storm across a handful of popular Caribbean destinations but was downgraded to a tropical depression before it could do much damage.

Tropical storm Erika left at least 20 people dead and dozens missing as it swept over the tiny Caribbean island nation of Dominica, also in August.

The Atlantic hurricane season, which runs from June 1 to November 30, sees peak activity in September.

But experts have said there was a 90 percent chance this year's season would be less active than usual.