Rural Fire Service members have been warned about crowdfunding for protective masks “without the appropriate authority” amid growing concern about resourcing levels of the state’s firefighting volunteers.

As fire crews battle more than 100 blazes across New South Wales, volunteers have been warned by the organisation’s leadership against using social media to crowdfund for equipment.

In an operational memo sent to brigade leaders on Wednesday, RFS deputy commissioner Rob Rogers said the organisation’s leadership was “concerned” that crowdfunding campaigns were being set up “without the appropriate authority”.

“NSW RFS firefighters are provided all necessary tools and equipment to undertake their work. This includes fire appliances and associated hoses, nozzles and all personal protection equipment including respiratory protection,” Rogers wrote in the memo.

“The cause promoted through some of these fundraising efforts has been to purchase P3 masks.

“The NSW RFS provides disposable P2 fire resistant masks to members. This provides a practical solution for managing exposure to bush fire smoke, when taking into account other risks.”

Several firefighting crews across the state have begun using crowdfunding sources and social media sites such as Facebook to appeal for funds to buy equipment.

Copacabana on the NSW central coast and Ingleside in Sydney’s north both started grassroots campaigns appealing for funds to buy more face masks.

This week Joe Arena, the treasurer of the Copacabana brigade, wrote on Facebook that the crew were “horrified” they have had to use RFS-issued P2-grade dust masks.

He said the crew was “completely exhausted” from battling blazes in the Hawkesbury region of the central coast but that volunteers “have no choice but to go out and fight fire with what we have”.

“In defence of the RFS, these are unprecedented conditions on a scale no one could have anticipated,” Arena wrote.

That message has now been deleted and replaced with a thank you message from the brigade.

It comes amid increasing concern about the resourcing of the volunteer firefighting force after a ferocious start to the bushfire season in which six people have been killed and more than 720 homes destroyed since last month.

Much of the concern relates to the protective masks given to firefighters. The Rogers memo cited a 2018 guideline published by the Australian Fire and Emergency Services Council which found P2 masks “remains the most practical” option and that P3 masks provided an “equivalent” amount of protection.

However, Rogers conceded that report “doesn’t take into consideration factors identified such as maintaining a face seal, breathing resistance and maintenance”.

“For the service to consider changing any of its provided firefighting equipment and apparel, we would require a full and comprehensive scientific research and evaluation process,” he wrote.

One RFS volunteer and physician, who asked to remain anonymous, told Guardian Australia that while well-fitted P2 masks were “somewhat effective”, there were “a lot of problems” using them in a fire ground where “getting a good fit is difficult”.

“As an experienced physician I have been dismayed at the level of smoke inhalation that I have had to endure in the last few weeks,” he said.

“The elastic straps frequently break. The mask becomes ineffective, and difficult to breathe through when wet, which is inevitable in a short time due to spray and sweat. Furthermore, fitting a separate mask and goggles over spectacles and then fitting a helmet leads to a tangle of straps, which is infuriating and potentially dangerous.

“While that might be manageable with regular mask replacement in a two-hour incident, it is unsatisfactory during 12-hour shifts, much of it in heavy smoke. Fire and Rescue have much better respiratory protection for professional firefighters.”

On Thursday, the prime minister, Scott Morrison, announced an $11m funding injection into the country’s aerial firefighting forc, after previously having rejected calls for more help for firefighters, saying they “want to be out there”.

But at a press conference later he said his office had raised the issue of crowdfunding with the NSW government, but seemed to dismiss social media fundraising as “misinformation”.

“Of course, that type of equipment is provided by the state government, and I would expect that these sorts of needs would be met out of those resources and they should be,” he said.

“I have noticed that over the course of these fires, and on social media, there have been lots of things … that are said and one of the issues that I’ve engaged with when I’ve gone into these incident response and control centres is what they often have to do is counter a lot of the misinformation and a lot of the commentary that has been provided on social media, which can cause unnecessary anxiety in communities.”

But Guardian Australia has been contacted by several RFS volunteers who have expressed concerns about resourcing.

Doug Rowley, captain of the Byron Bay RFS station, said his brigade was using donations to purchase facemarks with a two-stage filter because of shortages in supply.

“The safety of our firefighters is paramount. The RFS will say the same thing: the first and major consideration in anything we do is the safety of our firefighters,” he said. “But it’s a moot point as to whether or not you’re getting the appropriate level of support from the RFS in terms of the consumable items.

“I went to the store to get the facemarks … and there were none. This store is designed to service six brigades – it’s probably equivalent to three garages [in size]. It’s absurd.”

Another RFS volunteer, Stewart, said standard issue equipment was often the “bare minimum”.

“It meets the basic standards but it’s not the best,” he said. “I’ve spent nearly $2,000 alone on upgrading my PPE to a higher standard – helmets, better goggles, things like equipment pouches, head-mounted torches, which aren’t standard issue or where the standard issue is the most basic.

“This is the heart of the issue: the people that volunteer and are in the RFS by their very nature just get on and do it, this-is-what-we-do kind of people.”

The RFS has been contacted for comment.