NORTHERN New South Wales can expect heavy rain and significant inland and coastal flooding all week.

The Weather Channel senior meteorologist Tom Saunders said the wet conditions would also affect Queensland.

"For many areas the rain will be the heaviest since last summer.

"Weekly rain totals are likely to exceed 100mm along the east coast from Cooktown to the New South Wales mid north coast.

"For south-east Queensland and north-east New South Wales the totals should exceed 200mm, prompting a flood alert for the Bellinger, Macleay and Hastings river valleys.

"Many areas of western Queensland will also see over 100mm of rain this week," Mr Saunders warned.

He said "the drenching" would result from a persistent easterly airstream off the Tasman and Coral Seas.

"A similar weather pattern will prevail over Qld and NSW until at least the weekend.

"Rain is already falling over northern NSW with Kempsey and Taree picking up 30mm since Sunday morning.

"Further north a thunderstorm soaked Townsville with 51mm in just two hours this morning.

"Inland regions of eastern Australia are also seeing thunderstorms.

"Hughenden was hammered by a fierce storm on Sunday night recording a phenomenal 34mm of rain in just 10 minutes and a wind gust of 170km/h; equivalent to winds near the eye of a Category Three Tropical Cyclone.

"Winds of this strength are extremely rare for any inland region on earth.

"We are not certain exactly when the rain will clear but it won't be until at least Sunday," Mr Saunders said.