"The archipelago will feel the first effects from late Thursday afternoon," the Portuguese meteorological office (IPMA) said in its latest update on the popular tourist destination.

Gabrielle, which was still classified as a Category 3 hurricane on Wednesday evening, is expected to lose momentum and reach the Azores from the west as a Category 1 hurricane, the IPMA said.

Later becoming a "post-tropical depression", Gabrielle will make landfall in mainland Portugal on Saturday.

On Thursday night, the eye of the storm will barrel through the Azores' two western islands and then its five central islands, which are on red alert.

The regional government has ordered schools and public buildings on the seven islands of the Western and Central Groups to close for 24 hours from 6:00 pm local time (1600 GMT).

The Eastern Group, comprising the two remaining islands in the archipelago and a cluster of islets, have not received similar orders.

Winds could attain 150 kph in the western islands of Flores and Corvo before strengthening to up to 200 kph in the central islands of Faial, Pico, Sao Jorge, Terceira and Graciosa.

The ocean is expected to be rough with swells of eight to 10 metres. Waves could reach heights of 14-18 metres.

The regional civil protection service has urged islanders to limit their movements to those strictly necessary, avoid all activity at sea and secure their homes by strengthening roofs, doors and windows.

The district of Santa Cruz das Flores, in the north of Flores island, remained calm on Thursday morning but local fishermen said they were afraid violent waves would damage the port.

Firefighters in Flores told an AFP photographer they were worried that the intense rainfall forecast for the evening might trigger landslides.