More than 200mm of rain could fall over parts of southeast NSW and far eastern Victoria during the next 48 hours, prompting warnings for both flash and riverine flooding.

A developing low pressure system will drive a sustained stream of blustery, rain-bearing winds onto the South Coast of NSW and Victoria's East Gippsland district on Thursday and Friday.

The sequence of satellite images below shows cloud and rain already starting to stream over this region on Thursday morning.

This rain will become heavier as the low pressure system develops near the southern half of the NSW coast today, with heavy rain and potentially severe thunderstorms likely to continue into Friday.

Forecast models suggest that accumulated falls during the 48 hours ending at midnight on Friday are likely to reach 100-200 mm in some areas between Mallacoota and Ulladulla. Six-hourly totals could push up to 70-100 mm during this time. Localised totals could be even higher than these ranges, particularly with thunderstorms.

Image: Forecast accumulated rain on Thursday and Friday, according to the ACCESS-G model.

This much rain would be enough to inundate the landscape and cause areas of flash flooding, which has prompted a severe weather warning in parts of both states.

The rain also poses a risk of riverine flooding, with flood watches in place across Victoria's Gippsland district and parts of the North East district, and the Werribee River catchment. A flood watch is also in effect for the South Coast, Snowy and Upper Murray and Mitta Mitta Rivers in NSW.

Be sure to check the latest weather and flood advisories as this severe weather event unfolds.