Severe storms, heavy rain and rising flood risks are sweeping across south-east and central Australia as a deep low-pressure system powers east.

Rain was already falling in South Australia, the southern Northern Territory on Monday but is expected to spread further east into Queensland, NSW and Victoria later in the day.

Forecaster Weatherzone said thunderstorms were likely to develop over parts of SA and the NT from Monday afternoon.

“As the system moves further east on Monday night and Tuesday, rain and storms will increase over Victoria, NSW and southern Queensland, with showers also lingering in parts of SA and Tasmania,” it wrote.

“Rain is likely to become heavy along the ranges in southern NSW and north-east Victoria from Monday night into Tuesday morning.”

The outlook has  prompted severe weather warnings for heavy rainfall and flash flooding in both states. There are flood watches across much of Victoria, with severe thunderstorms possible over a broad corridor stretching from northern Victoria through western NSW and into southern Queensland on Tuesday.

Bureau of Meterology Senior meteorologist David Crockett said the low would drive three days of widespread rain and storms “across a vast area of south-east and central Australia”.

The system developed over Western Australia on Saturday and has already delivered widespread rain and thunderstorms across the west, western SA and the southern Northern Territory, including up to 30 millimetres in Alice Springs on Sunday.

The system was expected to move over SA’s Eyre and Yorke peninsulas before passing near Adelaide and the hills, with higher totals possible over already saturated catchments.

“Many of those areas, particularly the Adelaide Hills, are quite wet already following recent rain … the creeks and rivers are ready to respond quickly to any further rainfall,” Crockett said.

The heaviest falls of 40-60 millimetres are expected early on Tuesday over the north-east Victorian ranges and the south-east ranges of NSW, particularly the alpine regions.

By later Tuesday and Wednesday the focus turns to eastern NSW and south-east Queensland, which can expect generally 5-15 millimetres, with higher totals along the NSW ranges.

“This could be the first severe storm of the season for some of those areas, depending on how the storms develop on Tuesday afternoon,” Crockett said.

Forecasters warn of a broad severe thunderstorm threat on Tuesday afternoon from northern Victoria through western NSW into south-western Queensland, with heavy rain, damaging winds and possible large hail.

Weatherzone said most of the thunderstorms associated with the low would come after the initial rain band because that was where the atmosphere will be most unstable.

“This means some areas may see a period of persistent rain followed by potentially severe thunderstorm activity,” it said.

The system will start moving off the east coast and out over the Tasman Sea from Wednesday, with rain and storms contracting to eastern NSW and south-east Queensland. Drier and calmer weather will return to eastern Australia from Thursday.

-with AAP