Floodwaters in the northern part of the state isolated more than 1,900 people and shut part of the Pacific Highway, ABC News reported.
Winds uprooted trees and affected power lines, causing approximately 4,500 homes to lose electricity.
"The seas are in turmoil, there's spume coming in, flowing into the park and we've had a fair bit of structural damage to a number of caravans and annexes," said Richard Adams, who runs seven caravan parks.
More than 800 calls for help kept the New South Wales State Emergency Service busy all night.
Flood warnings are in place for six rivers across the area and high wind and huge waves pound the coastline.
The towns of Thora, Bellingen, Murwillumbah and Mullumbimby experienced minor flooding, ABC said.
Volunteers sandbagged homes and businesses.
A man who was trying to drive through a flooded creek at Murwillumbah, near Byron Bay, was rescued after he was forced to stop, climb onto the roof of his car and call for help, the State Emergency Service said.