Northern Ireland's First Minister is being treated in hospital after suffering a suspected heart attack.

Peter Robinson, 66, underwent a procedure at Belfast's Royal Victoria Hospital earlier today.

He was transferred in an ambulance to the RVH's specialist cardiac unit after seeking treatment at the Ulster Hospital which is close to his home in the Castlereagh hills.

A spokeswoman for the Belfast Health and Social Care Trust confirmed: "Mr Robinson underwent a procedure this morning and is currently recovering in the Royal Victoria Hospital."

His admission comes on the eve of a crucial debate on welfare reform which has been threatening to collapse the power-sharing institutions at Stormont.

The RVH, in west Belfast, is Northern Ireland's largest hospital and is the main centre for cardiology.

A DUP statement said: "The First Minister felt unwell this morning and has been admitted to the hospital for some further tests."

Messages of good will have flooded in from across the UK, Ireland and America throughout much of the day.

British Prime Minister David Cameron was among the first politicians to express concern.

He said on Twitter: "My best wishes to Northern Ireland's First Minister Peter Robinson who is in hospital. I hope he has a speedy recovery."

Scottish First Minister Nicola Sturgeon, Northern Ireland Secretary Theresa Villiers and Sinn Féin Deputy First Minister Martin McGuinness also used Twitter to show their support.

Mr McGuinness said: "Concerned to hear First Minister Peter Robinson has been admitted to hospital. My thoughts & prayers are with him, Iris & family."

Mr Robinson, a father of three, has been leader of the Democratic Unionist Party (DUP) and First Minister since 2008.

In contrast to his predecessor, the Ian Paisley, his tenure has been characterised by mixed relations with his coalition partners, Sinn Féin.

DUP colleagues including the party's deputy leader Nigel Dodds, new East Belfast MP Gavin Robinson, North Antrim MP Ian Paisley Jr and former health minister Jim Wells have also added their best wishes.

Mr Dodds said he believed the First Minister had taken ill during the night.

Members of the Robinson family, including disgraced former Strangford MLA Iris Robinson whose affair with a teenager sparked a scandal which almost ruined her husband's 35-year political career when it was exposed in 2010, have asked for privacy, as they rally round.

As leader of Stormont's largest party Mr Robinson has been under significant pressure in recent months not least because of the welfare reform wrangle.

His hospital admission means he is likely to miss tomorrow's key debate on proposed changes to the benefits system.

Nationalists have vowed to veto the move and have deployed measures to block the Welfare Reform Bill when it is brought to the floor of the Assembly.

Mr Robinson has warned that the Executive faces financial meltdown and said he would seek to hand welfare powers back to London if the Bill was rejected.

The DUP also endured a difficult election campaign and was forced to enter a pact with the Ulster Unionists to safeguard seats.

Further pressure was added when former health minister Jim Wells resigned after a furore about comments he made linking same sex marriage to child abuse. The resignation meant Mr Robinson had to re-shuffle his top team.

Mr Wells said he could not recall Mr Robinson having a sick day in 40 years.

He said: "I have known Peter since 1975 and I cannot remember him ever having a day off sick.

"He always struck me as being fit and healthy, so it was a real surprise to hear the news.

"The party will be 100% behind me in wishing him well. We hope he will be back on his feet as soon as possible.

"It will be strange not having him with us at this crucial vote tomorrow - assuming he won't be there. I wouldn't put it past him to bounce back quickly."