First Minister Peter Robinson and deputy First Minister Martin McGuinness said they were deeply affected by the deaths and those of three other people.

Mr Robinson said: "Seven people have been killed including four police officers who died as the result of a tragic accident whilst serving their community. My thoughts and prayers are with all the victims' families and loved ones."

Mr McGuinness said: "This has been a tragic weekend on our roads, I would call on all motorists to exercise caution to avoid any further loss of life this weekend. I would like to pass on my condolences to all the victims' families at this very difficult time."

Secretary of State Shaun Woodward said: "The police do difficult and often dangerous work to protect the community and keep it safe.

"It is at times like this that the huge debt that we all owe them is brought home in a particularly shocking and cruel way."

Ulster Unionist deputy leader Danny Kennedy expressed his "profound shock and sorrow" at the early morning accident, which he said was a reminder to the entire community of the great service and public duty carried out by police officers at all times.

"Most of all this loss will be felt by the immediate family and relatives of the four officers and I want to assure them of all our thoughts and prayers at this very difficult time."

The DUP's four Policing Board members Tom Buchanan, Ian Paisley Jnr, Jimmy Spratt and Peter Weir issued a joint statement: "While the exact circumstances of this tragedy are unclear we must remember that there are families in the deepest of grief.

"We want to assure them of our thoughts and prayers at this time of loss and heartache."

South Down SDLP MLA Margaret Ritchie said: "The community of Warrenpoint, Rostrevor and the wider Mournes area will be shocked at the nature of this loss and will stand shoulder to shoulder with the families of these officers in their tragic loss."

Local SDLP MP Eddie McGrady said the officers died in the service of the community and "words cannot describe the deep sense of despair and loss" that their families must be feeling.

TUV MEP Jim Allister said the deaths should remind people of the debt they owe to police.

"The terrible loss of life in the death of four gallant police officers as they served the community is truly shocking."

He added: "The loss in the close-knit Mourne community, which throughout the Troubles bore more than its share of security force losses, is palpable."

Alliance Party justice spokesman, Stephen Farry, said: "This is a huge tragedy not just for the police family but the whole community in Northern Ireland.

"These officers were out on a difficult night keeping the rest of us safe in our beds."