In his statement on Wednesday, Burrows described Nesbitt as approaching his ministerial position "with seriousness, integrity and a determination" and said the direction he set on tackling issues would continue.

In a statement on Tuesday, a UUP spokesperson thanked Nesbitt "sincerely for his service and for the leadership he has given to our health and social care workforce".

"Mike took on one of the most difficult briefs in government with a genuine determination to make health and social care better for everyone in Northern Ireland.

"From beginning the shift towards a neighbourhood model of care, to putting health inequalities at the centre of policy, he leaves a significant legacy, not least the progress made on some of Northern Ireland's longest waiting lists."

It is unclear who will take over as health minister but Nesbitt's decision to quit leaves the party seven days to nominate a replacement.

Speaking on Radio Ulster's The Nolan Show, the DUP's Paul Frew said that if the UUP "walked away" from the health ministry, the D'Hondt system would be triggered, and he believed the DUP would be the next party in line for that ministry.

"Of course we would then put a minister in place," he added.

Dr Alan Stout, who chairs the British Medical Association's (BMA) Northern Ireland Council, said he has "huge respect" for Nesbitt for the "clinically led principles" that he has had on Causeway Hospital, adding that he put "patient safety above politics".

Speaking on BBC Radio Ulster's Good Morning Ulster programme, he said: "It's always for too easy to play the populism card, to promise what is undeliverable.

He said politicians who are prepared to stand up and make the difficult decisions are what is needed.

The chair of Stormont's health committee, Phillip McGuigan, said he was convening an urgent meeting of the committee.

"The loss of Mike Nesbitt...comes at a time when our health and social care system is already under immense pressure.

"Patients and staff need leadership, stability and clarity," the Sinn Féin MLA said, adding that the committee needs to understand what happens next and how it can help play a positive role."