Tasmanian environmentalists have joined a global campaign to spend their Saturday night perched in some of the state's best-known tree tops.

A platform is lifted into place for Canopy Campout, in Tasmania. ( Supplied: Dan Broun )

Over 40 "canopy campouts" were held worldwide to raise funds and awareness for threatened rainforests around the world, and particularly in Borneo.

Participants in Tasmania gathered at two locations — in the Frankland River forest in the Tarkine region on the state's north-west, and on Kunanyi/Mount Wellington in Hobart, in a Eucalyptus regnans, which is recorded as the world's second-tallest tree species and Australia's tallest, as well as being the world's tallest flowering plant.

Those taking part braved the elements, with sub-zero temperatures hitting overnight.

Steve Pearce from Tasmania's The Tree Projects spent the night in the Eucalyptus regnans on Mount Wellington.

"We tried to camp up there on Friday night as well, but the weather was pretty horrible," he said.

"We were camped in a device called a portaledge, which is basically a tent for the trees."

The temperature dropped below zero in the Frankland River area. ( Supplied: Dan Broun )

Mr Pearce said he did manage to get some sleep.

"It was pretty breezy and cold, it wasn't what most people consider an ideal experience, but it was an experience all the same," he said.

Mr Pearce said the money he raised would go to the World Land Trust.

"They are purchasing a huge swathe of Bornean rainforest, Borneo has one of the fastest land clearing rates in the world," he said.

The Big Canopy Campout website described the event as "celebrating the beauty and diversity of forests and valuing them through adventure".

The event kicked off across Australia and New Zealand, with other world regions following as the sun set.