The situation with the low-pressure system moving south from Queensland into Northern NSW overnight is intensifying with the Bureau of Meteorology releasing a Heavy Rainfall Warning for the Northern Rivers.

The expected rainfall total has increased to 80-150mm after initially forecast at 25-45mm only days ago before increasing to 45-80mm.

This rainfall may cause moderate to possible major flooding along the Wilsons River from Sunday, with minor to major flooding possible along the Tweed and Richmond Rivers.

The Bureau said: A low-pressure system off the Capricornia coast in Queensland is expected to continue to develop and move slowly south to southeast over the next 24 hours and remain just offshore from southeast Queensland by Sunday morning.

HEAVY RAINFALL which may lead to FLASH FLOODING is forecast to affect the Northern Rivers District and parts of the Mid North Coast and Northern Tablelands Forecast Districts. Six-hourly rainfall totals between 90 to 150 mm are likely to develop from early Sunday morning. 24-hourly rainfall totals between 100 to 150 mm are likely with falls up to 300 mm possible, especially along the coast and across the ranges.

(The Bureau of Meteorology weather radar showing the low-pressure system coming our way from Queensland at 1pm Saturday)

Locally INTENSE RAINFALL which may lead to DANGEROUS AND LIFE-THREATENING FLASH FLOODING is also possible during this period with six-hourly rainfall totals up to 200 mm. The highest risk areas are over coastal areas and the ranges. A separate Severe Thunderstorm Warning will be issued if very dangerous thunderstorms with intense rainfall are detected.

A Flood Watch is current for the Richmond, Wilsons and Tweed and Rouse Rivers, while a minor flood warning remains for the Orara River

NSW warning products: http://www.bom.gov.au/nsw/warnings/index.shtml

Locations that may be affected include Lismore, Grafton, Casino, Kyogle, Yamba and Maclean.

The State Emergency Service advises that people should:

* Don't drive, ride or walk through flood water.

* Keep clear of creeks and storm drains.

* If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue.

* Be aware that run-off from rainfall in fire affected areas may behave differently and be more rapid. It may also contain debris such as ash, soil, trees and rocks.

* After bushfires, heavy rain and the loss of foliage can make the ground soft and heavy, leading to a greater chance of landslides.

* Stay vigilant and monitor conditions. Note that the landscape may have changed following bushfires.

* For emergency help in floods and storms, ring your local SES Unit on 132 500.

The next Severe Weather Warning will be issued by 5:00 pm AEDT Saturday.