Ireland's national weather service says the country has seen 114 mph wind gusts, the highest ever recorded on the island.
A red wind warning has been issued for the whole of the Republic of Ireland, with Met Éireann warning of a possible "danger to life". The alert comes into effect at varying times from 02:00 on Friday and will end at varying times. Met Éireann has warned that "severe, damaging and destructive winds" are expected, with gusts of up to 130km/h.
Storm Éowyn has claimed two victims after wind speeds in the UK hit 100mph - the Met Office still has several weather warnings in place this evening as there continues to be a 'danger to life'
Millions of mobile phone users got an emergency alert as people in Scotland and Northern Ireland warned to stay indoors and schools close
The Met Office issued the red alert for Northern Ireland until 14:00 GMT, emphasizing the severity of the situation.
About 283,000 customers are without power in Northern Ireland - and more than 700,000 in the Republic of Ireland Wind speed records have been broken in the Republic of Ireland with hurricane-force sustained winds of 85 mph (137 km/h) at Mace Head, County Galway
Met Office deputy chief meteorologist Mike Silverstone said: “The strongest gusts are likely to be felt across parts of Northern Ireland, northern England, north-western Wales and western Scotland, where exposed sites could get gusts in excess of 80mph, which has the potential to cause impacts for those in these areas.
More than a million homes and businesses without power across island of Ireland - ESB Networks in Ireland and NIE Networks say they expect significant further outages as Storm Eowyn continues to batter parts of the island.
Winds reached 100mph as Storm Eowyn left one person dead, more than a million people without power and caused significant travel disruption across the UK and Ireland. Rail services, flights and ferries have been cancelled across the country as rare red weather warnings are in place on Friday in Scotland.
Across the border Met Eireann has issued a rare nationwide red warning for wind across the Republic of Ireland. A Met Office spokesperson said peak rush hour wind speeds of 80-90 miles per hour are expected across Northern Ireland, with up to 100mph in some exposed locations.
Storm Éowyn has begun battering Northern Ireland, bringing with it winds of more than 90mph and leaving 93,000 homes and businesses without power. Northern Ireland has seen the highest gust in 27 years.