Homeowners are being warned to avoid using tree lopping services that go door-to-door, with national industry groups saying they could cost people money and exacerbate the risk of falling trees.

Transient tree loppers have been in the spotlight since it was discovered multiple Sydney outfits were operating in the New South Wales Hunter region, having travelled from COVID hotspots under lockdown.

"Tree lopper" is a term used by the industry to define an unqualified person who cuts trees for a fee, while an arborist is the term for a certified professional.

Mark Hartley from Arboriculture Australia said because the industry was "completely unregulated" there has been a growth in unskilled, untrained, and sometimes unethical, groups operating out of parts of Sydney, Brisbane and Melbourne, and door-knocking was a red flag.

"Qualified arborists usually aren't trying to get the job done quickly," he said.

"If you've got someone knocking on your door and wanting to do the work almost straight away, there's a good chance that there's something wrong there."

Increased risk

NSW Fair Trading said door-knocking tree loppers rarely held appropriate insurance, usually required cash payments and often left work unfinished, particularly if they received upfront payment.

"It is not uncommon for members of these groups to advise consumers that otherwise healthy trees are diseased and must be removed," it said.

"There have also been identified incidences of members of these groups returning and targeting consumers they identify as vulnerable, often offering other urgent services in an attempt to gain further payments."

Mr Hartley said consumers should also be aware that arbitrarily cutting back trees could make them more dangerous.

"Somebody who is not trained will just make cuts and in many cases those cuts will be inappropriately located and will cause harm to the tree and potentially exacerbate the problem," he said.

"Sometimes a person is thinking that they're reducing the risk associated with the tree, but it can have the opposite impact."

They work 'fast and furious'

President of the Tree Contractors Association of Australia Jim McArdle described some elements of the industry as "door-knocking criminals" who in the past had impersonated his business to steal clients and deliberately poisoned trees to get jobs.

"I would certainly discourage people from accepting a quote from a door-knocker, you cannot qualify them on information," he said.

"The only reason a qualified arborist would knock on your door is if they've noticed something that's extremely worrying, like a branch into power lines, as they're walking past."

Newcastle consulting arborist Ian McKenzie said door-knocking tree loppers often ran a "fast and furious" operation, quickly moving from one council to the next to avoid scrutiny.

"Mostly if you're going to have a tree pruned or removed you need to get approval from council first," he said.

"So it's just not an industry that works on a door-to-door basis."

Illegal tree removals

Mr Hartley said unscrupulous tree loppers were responsible for a significant number of illegal tree removals in Australia, and that homeowners were often fined if the contractor could not be found.

"Often times what ends up happening is the house holder ends up carrying the baby," he said.

Mr McKenzie said it was an ongoing frustration that local councils were not more proactive in cracking down.

He said the group from western Sydney twice knocked on his door in Mayfield last month and he reported them to Newcastle City Council on August 18 for the suspected illegal removal a palm tree on a neighbouring property.

Council responded to Mr McKenzie's complaint seven days later via email to confirm no permit had been applied for to remove the palm.

"I think it's imperative that when council gets a call about an illegal tree removal that they react quickly because they need to gather the evidence and if they don't get out there immediately it's very difficult, they need to catch people in the act," Mr McKenzie said.

"And in this situation, with COVID, where people were knocking door-to-door, that should have been raising alarm bells for council too."

Several in the group were later diagnosed with COVID-19 and health authorities said they were possibly infectious in the community between August 15 and 31.

Prosecution unlikely

In a statement Newcastle City Council said it was attempting to investigate the illegal removal of the palm tree.

"However, given the resident was not able to provide the name of the company who undertook the tree removal, licence plate number of their truck or any detail to assist in identifying the illegal work, the likelihood of prosecution is low," it said.

Mr McKenzie said no one from Council attempted to find out more detail from him.

The tree loppers could not be reached for comment. Police are still investigating whether their activities were in breach of Public Health Orders.