Intense storms over parts of the New South Wales north coast have flooded farmland and damaged crops.

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The community of New Italy, near Woodburn, received almost half a metre of rain on Saturday alone, while Dorrigo had 430 millimetres over the weekend.

Woodburn State Emergency Service (SES) unit controller Jim McCormack, also a beef farmer in the district, said it had been more than 40 years since a rain event like this.

"The system just sat over the top of us for a number of hours and just belted us with everything it had," Mr McCormack said.

"It was so intense for that five or six hour period on Saturday morning, it caused all sorts of issues for our SES unit as well, but people are seeing water where they have never seen water for a long, long time."

Mr McCormack said a fall of 443 millimetres at New Italy resulted in water backing up in places that had not been flooded for years.

On the Macleay River, east of Kempsey on the mid-north coast, cattle producers are on alert for rising waters.

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Farmer Richard Fischer had over 94 millimetres fall at his property near Bellbrook over six hours on Saturday night.

He is land-locked on his property with about five metres of water covering the Macleay Bridge.

"My big concern is our cattle on the lower Macleay," he said.

"Hopefully the river will keep within its bounds and they won't have to open the flood gates.

"We can handle the rainwater, but the muddy flood waters will deteriorate any growth in the grass and pastures down there until at least the spring, early summer.

"We don't want that to happen."

Road damage after almost half a metre of rain in one day caused flash flooding at New Italy. ( Supplied: Keryn Clapham )

On the Kalang River, near Urunga on the mid-north coast, oyster farmer John Lindsay said his production would be pushed back by about a month because of the flooding.

"We are usually in a mad rush to tidy it all up and get as many oysters out as we can, but we aren't going to harvest anything for the last month I'd say," he said.

Mr Lindsay said the season had been going particularly well until now.

"With the amount of fresh water we have gotten in the river, we can't harvest our oysters and this is our last chance to make a dollar before they spawn out for the winter," he said.

The rain has been widely welcomed by primary producers after an extended dry period on the state's north coast.