Assistant ministers Chris Picton and Katrine Hildyard will be elevated to Cabinet, with Premier Jay Weatherill set to unveil a refreshed ministry six months out from the South Australian election.

Labor's caucus met at Parliament House this morning to elect the southern suburbs MPs to the vacancies left by Health Minister Jack Snelling and Mental Health Minister Leesa Vlahos.

Their departures will spark a wider reshuffle of the Cabinet, with Police Minister Peter Malinauskas tipped as a likely replacement for Mr Snelling.

Backbenchers Annabel Digance and Nat Cook will take positions as assistant ministers, while Treasurer Tom Koutsantonis will take over Mr Snelling's responsibilities as the Leader of Government Business in the House of Assembly.

The new ministry will be unveiled at Government House this afternoon.

Ms Vlahos announced she would be stepping down from the mental health portfolio overnight just hours after Mr Snelling resigned as health minister.

Ms Vlahos was plagued by problems at the now-closed state-run Oakden nursing home over the poor treatment of dementia patients.

She said she would not be quitting politics altogether and intended to stay on past next year's state election in the Upper House.

Mr Snelling resigned yesterday amid ongoing scrutiny over unpopular changes to the state's public hospital system.

Despite the criticism, Mr Snelling said he was proud of his achievements, including opening the new Royal Adelaide Hospital (RAH).

"I guess the decision for me was is it time now to hand that baton on to someone else and the completion of the hospital I think provides an appropriate moment for that to happen," he said.

"Of course there's always things that you could have done better or could have done differently, but all in all I look back on my career with enormous satisfaction."

Mr Snelling will not be seeking re-election.

Health system in state of chaos: Opposition

Opposition Leader Steven Marshall said Mr Snelling and Ms Vlahos' resignations are a vote of no confidence in Premier Jay Weatherill's Government.

He said Mr Snelling had left the state's health system in chaos.

"The health system in South Australia is in a complete and utter mess and half way through the transition to the new RAH the health minister resigns. It is a hopeless Government," Mr Marshall said.

"There are a number of issues which are confronting the health system in South Australia — the ramping, the Oakden ICAC inquiry."

He said it was interesting that two ministers responsible for Oakden have resigned ahead of the release of the anti-corruption watchdog's report into the issues.

"South Australia needs a single health minister," he said.

Resignations chance to refresh: Premier

"Labor has managed this portfolio in a chaotic fashion, with three ministers responsible for health," Mr Marshall said.

"Jack Snelling, Leesa Vlahos and Zoe Bettison have all been looking after health on a part-time basis and we can see the results."

Mr Weatherill described the two resignations as an opportunity to refresh his team ahead of next year's state election.

"There is no doubt that it gives us an opportunity to look at the issues associated with their portfolios with fresh eyes and to meet with the constituencies and to speak to the people affected in their areas," he said.