Arborists started cutting down a beloved Moreton Bay fig tree in Randwick, known locally as the "Tree of Knowledge", for construction of Sydney's eastern suburbs light rail line on Sunday night.

About 40 people gathered at the intersection of Wansey Road and High Street where the tree, believed to be about 150 years old, had been enclosed by two-metre-high fencing earlier in the afternoon.

Randwick City councillors Kathy Neilson and Tony Bowen, and NSW Greens MP Mehreen Faruqi stood alongside residents on the street after work to cut down the tree began about 6.30pm.

Ms Neilson, who was involved in discussions between Randwick City Council, the University of NSW and Transport for NSW, had been under the impression that Transport for NSW was considering a reroute of the light rail line to save the tree.

"I can't believe it," Ms Neilson said. "The understanding was that the trees would be safe until November.

"Here we are on a Sunday night, it's school holidays, the university is on holiday, the tree is coming down and there's no way to stop it."

Early on Monday, the tree remained standing, but a number of branches had been cut off. It was not immediately clear whether work would continue on Monday.

Transport for NSW has been contacted for comment.

Randwick resident Greg Vankuyk said he saw the fences being erected when he drove by about 4pm, and asked the workers what was happening.

"They said it was roadwork," Mr Vankuyk said.

"I got a ring at 7pm from a friend saying they were cutting the tree down.

"There could be wildlife in the hollows of the trees but we can't see because they've got these high fences. It's a magnificent tree and what's gone on is absolutely disgusting."

In May, more than 400 protesters gathered at Moore Park at a rally calling for a parliamentary inquiry to stop the felling of the Anzac Parade fig trees.

CBD transport co-ordinator general Marg Prendergast said last week that she understood the emotion surrounding the removal of trees and that at least 81 of the 112 figs on Anzac Parade would remain once the light rail line was completed.

"It's the 21st century," Ms Faruqi said as the Tree of Knowledge was being sawn down. "We can plan for public transport and plan for the environment, as well."

150+ years to grow but only a few hours to destroy the tree of knowledge @UNSW @smh @SydneysTrees pic.twitter.com/ZpQlWjybNq— Mehreen Faruqi (@MehreenFaruqi) July 10, 2016

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