Lorenzo, the most northerly and most easterly large hurricane ever to form over the Atlantic Ocean, is now headed straight for Ireland.

It has weakened to a Category 1 hurricane, but is expected to be a strong extratropical cyclone when it approaches Ireland tomorrow evening, according to the US National Hurricane Centre (NHC).

Meteorologists were warning this week that large swells generated by Hurricane Lorenzo would continue to spread across much of the North Atlantic basin during the next few days, producing life threatening swells and rip currents.

The hurricane reached Portugal's Azores islands in the early hours of this morning, causing power outages and knocking down trees across the mid-Atlantic archipelago, authorities said.

Packing 150km/h winds, it was predicted likely to cause life-threatening surf and rip current conditions there, with only a slow weakening forecast over the next 48 hours, the Miami-based National Hurricane Center said.

The nine islands of the Azores lie about 1,500km west of the Portuguese mainland and are home to nearly 250,000 people.

"This might be the strongest (hurricane) in the last 20 years," said Carlos Neves, head of the Azores' civil protection authority. "Although it shifted slightly in recent days to the west, it has affected us in a very aggressive way."

The NHC said hurricane-force winds battered the western Azores, while the archipelago's central islands experienced tropical storm conditions.

Hurricane warnings were in effect for the islands of Flores, Corvo, Faial, Pico, Sao Jorge, Graciosa and Terceira.

No one has been injured although there have been cases of trees falling down, Civil Protection said.

Mr Neves said power cuts and mobile network problems were reported on Flores, one of the worst-hit islands.

"We hope to fix those issues in the next few days," Mr Neves said.

Lorenzo briefly became a Category 5 hurricane at the weekend, the strongest on record this far north and east in the Atlantic, but it has since been downgraded, striking the Azores as a Category 1.

Schools and non-emergency services were closed across the Azores today, the regional government said, with ports on some islands also shut. Authorities closed numerous streets and roads.

NHC said Lorenzo will move away from the Azores and closer to Ireland tomorrow evening.

"Lorenzo is expected to be a strong extra-tropical cyclone when it approaches Ireland," NHC added.