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An evacuation warning - different from an evacuation order - is currently in place for the CBD, the SES has announced.

"The NSW SES is advising people in Picton CBD to prepare to evacuate," The SES Wollondilly Unit posted on Facebook.

"As a result of rising flood waters, people within the Picton CBD should prepare to evacuate.

"Residents should monitor the situation and be prepared to evacuated when instructed to do so.

"The NSW SES will issue a Flood Evacuation Order if evacuation is required."

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The evacuation warning went out at 9am.

If Stonequarry Creek continues to rise, there may be flooding of roads, sewerage lines and power may be lost, and properties may be inundated.

The creek did not flood into the town during last month's weather event.

The weather has seen Menangle Bridge closed this morning, and Douglas Park Causeway underwater overnight.

Woodbridge Road at Menangle is also affected.

There is a moderate to major flood warning in place for the Upper Nepean River.

"The [Nepean River at Menangle] is likely to exceed the moderate flood level (9.20 m) around 01:00 pm Thursday and may reach the major flood level (12.20 m) Thursday evening," Wollondilly SES Unit posted.

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"The Nepean River at Camden Weir is likely to exceed the minor flood level (6.80 m) around 03:00 pm Thursday. The river level may reach the moderate flood level (8.30 m) overnight Thursday into Friday.

"The Nepean River at Wallacia Weir may reach the minor flood level (5.00 m) overnight Friday into Saturday. Further rises to the moderate level are possible."

Several roads in Camden are also affected by severe weather and localised flooding.

Cawdor Road/Sheathers Lane at Camden and Smalls Road at Grasmere are both closed, while Little Sandy Bridge (Camden) and Macquarie Grove Bridge (Kirkham) are also closed.

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