Labour has moved to clarify its Welsh NHS plans after rivals claimed it cast doubt on the future of hospital trusts.
Brian Gibbons was talking in a meeting with health professionals
Several people claimed Brian Gibbons, the health minister since 2005, told a meeting that trust status had reached the end of its life.
Tories called it "astonishing", and Lib Dems asked if Labour would scrap the trusts if it won the assembly election.
But Labour said it had already made clear in its manifesto that it wanted more accountable NHS trust boards.
The issue arose on a day ITV published an NOP poll of voting intentions across the 40 constituencies.
It indicated Labour would receive 32% of the vote, down four points since a similar poll three weeks ago, and Plaid Cymru 26%, up six.
The survey gave the Conservatives a 19% share of the vote, down four, with the Liberal Democrats static on 15%.
On the Welsh NHS, Dr Gibbons, who has been assembly government health minister since 2005, was reported to have made the comments at a meeting of health professionals on Wednesday.
There are 14 health trusts in Wales, which are mainly responsible for delivering services, including hospital care.
Siobhan McClelland, a health economist, told BBC Radio's Good Morning Wales that "yesterday, at a hustings for the Institute of Healthcare Management, Brian Gibbons said that he felt that (NHS) trusts had reached the end of their life".
She told the programme that it was not clear what he meant by that, and Dr Gibbons did not expand upon his comments.
Leading members of the Conservatives, Liberal Democrats and Plaid Cymru were at the meeting and said they had also heard the comments.
Some of those attending the event said the audience reacted with shock to the comments.
There are 14 health trusts in Wales and 22 local health boards
Conservative health spokesman Jonathan Morgan, whose party proposes to scrap Wales' 22 local health boards, said: "This is an absolutely astonishing claim to make, especially at a time when people across Wales are worried about the future of local hospital services.
"Brian Gibbons needs to clarify his party's position immediately. There is no mention of abolishing NHS trusts in Labour's assembly election manifesto.
"Welsh Conservatives have been up-front and honest in our manifesto about our plans for the structure of the National Health Service. It is absolutely vital that Brian Gibbons and the Labour Party do the same."
Liberal Democrat Jenny Randerson said: "Brian Gibbons has let the cat out of the bag. Now Labour should come clean on what further organisational change they are plotting for the NHS.
"Are they proposing to scrap the NHS trusts? There's certainly nothing about that in their manifesto, but that's one way of interpreting Brian Gibbons' words.
"We're offering people a no-meddling guarantee at this election. We want to let doctors, nurses, physiotherapists and pharmacists get on with the job."
Plaid Cymru's Leanne Wood said: "Clearly health services need to be organised as efficiently as they possibly can.
"I think Plaid Cymru would welcome a review of the situation. But I think we would be concerned about any costly reorganisation now at this stage which would obviously cause more difficulties for staff and patients."
But Labour insisted it was not going to embark on a major NHS reorganisation or scrap hospital trusts.
A Labour spokeswoman said the party simply wanted to make trusts' boards more accountable, and that Dr Gibbons was talking about "reform without reorganising the governance of NHS trusts".
A Labour spokeswoman said: "Our manifesto makes it clear that the governance of trusts in their current form needs reform, to make the boards more responsive to the local populations they serve and to the Welsh Assembly Government, and to clarify where accountabilities lie.
"It's all about the way they are overseen and making them more accountable."
Labour's manifesto said: "We will reform the way NHS trusts are managed so as to end for good the Tory model of competition for patients and resources and improve trust accountability to local communities."
It adds that the Welsh NHS would be defined by "collaboration, not competition" and an independent analysis would be commissioned into the way the NHS is managed.
The Royal College of Nursing said nobody wanted more NHS reorganisation, but its structure needed streamlining over time.