A koala habitat 50 per cent larger than the Royal National Park has been destroyed by logging, according to a new conservation report.

The report titled Clearing Koalas Away by conservationist Dailan Pugh, says more than 23,000 hectares of koala habitat near Coffs Harbour has been "virtually cleared".

"They're hitting them really hard. We're looking at about 40 per cent of koala habitat in state forests," he said.

"Their own modelling is showing these areas are important but they're ignoring that."

Mr Pugh, an environmentalist for over 40 years, sourced the forestry data under freedom of information (FOI) legislation, in a bid to measure logging against known koala habitats.

Last year, then-environment minister Mark Speakman admitted "intensive harvesting" on the North Coast was "not consistent" with regulations, and said the Environment Protection Authority was investigating.

An EPA spokesperson declined to answer questions, but said "current rules are over 15 years old and lack clarity in important areas, including intensive harvesting".

Recent studies suggest less than 9,000 koalas survive on the North Coast, a 50 per cent decline in the past 20 years.

Habitat loss is widely acknowledged as a driver of the decline.

A picture taken in March 2016 shows trees that have been cut down in the Kerewong State Forrest. ( ABC News: Lyn Orrego )

Evidence of over-logging near koalas

Mr Pugh said a sustainable logging method called "single-tree selection" is being misused by Forestry Corporation.

Single-tree selection permits the selective harvest of just 40 per cent of eucalypts trees in a logging zone — leaving 60 per cent of trees as off-limits.

But the off-limits status is temporary, and evidence shows these trees are heavily logged in later operations.

The reports highlights examples like Kerewong State Forest, with photos showing the heavy clearing of a mapped koala habitat.

A large part of the "offset" area had been intensively logged in the Kerewong State Forest. ( Supplied )

Forestry data and satellite maps show the neighbouring off-limits area was itself heavily logged in 2009, removing feed-trees and destroying habitat.

Mr Pugh claimed the practice breached environmental laws.

"It's definitely clear-felling and it's totally illegal," he said.

"They're meant to retain 60 per cent of the area, and they're in there taking 80 to 90 per cent without doubt."

A spokesperson for Environment Minister Gabrielle Upton said she was committed to "stabilise and ultimately increase the numbers of koalas" and is "developing a whole-of-government koala strategy" to complement its conservation work.