Remote towns may be cut off, requiring food and medical drops, by heavy rain that has begun falling in South Australia's north, the State Emergency Service (SES) says.

The SES has begun distributing 15,000 sandbags, including in Port Pirie, after the weather bureau issued a flood watch and severe weather warning for parts of the state.

Tieyon Station, 500 kilometres north-west of Oodnadatta, has so far recorded the highest rainfall with about 120 millimetres.

Rain has already started to wash out roads and the SES has warned creeks in the Flinders Ranges, Mid North, Mount Lofty Ranges and Fleurieu Peninsula may burst their banks.

"The outback communities are very resilient - they tend to be people who've seen it all before, be it bushfires, storms and everything else and they tend to be self sufficient," SES acting chief officer Dermot Barry said.

"Our concern is that they'll become isolated and in time we may have to support them with either food drops or medical drops."

Mount Sarah Station has had 70 millimetres of rain as of 10:00am this morning. ( Audience submitted: Cameron Williams )

The transport department has closed a number of roads in the state's outback due to flooding, including the Birdsville Track from Mungeranie to Marree, the Oodnadatta Track from William Creek to Marree and the Strzelecki Track from Mount Hopeless to Lyndhurst.

The weather bureau said parts of the state's north could receive a further 100 millimetres of rain over the weekend.

Gorge Road in the Adelaide Hills, which was closed during the Sampson Flat fire, will remain shut over the weekend because of the potential of rock falls in the slippery conditions.

The bureau had previously warned that the current system had the potential to produce the most rain over the state since 1984.

But acting regional director, John Nairn, later said the storm could bring the highest rainfall in 40 years.

"The pattern that we are seeing evolve is a very similar pattern to the 1974 pattern," he said.

"We definitely have the right ingredients to produce a lot of rain as to whether we get up in that top end, we will have to wait and see."

Adelaide Hills bushfire continues to burn

Rain has helped crews battling a bushfire that has been burning north-east of Adelaide for eight days, but Country Fire Service (CFS) deputy chief officer Andrew Lawson said too much could affect water supplies.

"We could expect a lot of rain in the fire area, which is going to cause the run off to run down through the catchment areas and possibly into the reservoirs, and SA Water are working on that at the moment to try and ensure the water quality is maintained," Mr Lawson said.

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SA Water's James Crocker said several hundred hay bales had been placed around Millbrook Reservoir to stop erosion washing too much ash and other dirt into the water.

"We've identified the six highest priority areas and we've focused on them," he said.

"If we get really intense rainfall as forecast then there's not really a lot we can do to stop it coming in from other areas."

The fire has been contained, but the CFS has warned numerous hot spots could reignite unburnt ground within the perimeter.

Former state government minister Karlene Maywald has been appointed to lead the recovery stage of the bushfire response.

Ms Maywald will be temporarily based at the Golden Grove Recreation Centre.

The Government said Ms Maywald would bring valuable skills and experience to the role and would work with affected residents to help them get back on their feet.

Patients and aged-care residents who were relocated when the fire came within kilometres of the Mount Pleasant and Gumeracha hospitals have begun returning to both facilities.

The fire, which has burned more than 12,500 hectares of land, has destroyed 27 homes and more than 100 outbuildings and sheds.

Premier Jay Weatherill has pledged $1 million worth of assistance, while Prime Minister Tony Abbott announced an Australian disaster recovery payment of $1,000 per adult and $400 per child for bushfire victims who lost their homes or had their homes severely damaged.

While some roads remain closed, others have been reopened to local residents only.

Investigations into the cause of the fire are ongoing as forensic investigators continue to examine a Sampson Flat property, in particular an area surrounding an incinerator.