The flood crisis continues across NSW and in southeast Queensland with thousands of people under evacuation orders and many areas still on high alert.

Intense rain has continued in NSW and Sydney's main water source, Warragamba Dam, has released around 600 gigalitres of water into the flooded river system.

More than 100mm of rain fell in multiple areas near the dam between 9am and 6pm on Wednesday.

About 130,000 homes are in the path of the overflowing dam.