SINGAPORE - Hiker Adrian Kuah was visiting the Singapore Quarry in Dairy Farm Nature Park on Sunday (July 11) when he saw a slab of the cliff face breaking off and falling into the lake.
He detailed the incident in a Facebook post on the same day. He said it happened without warning, save for a loud crash.
He also attached a photo he took of the cliff face after the occurrence.
In response to The Straits Times' queries, Mr Kuah said the incident happened a few minutes before 4.58pm.
The director of the Futures Office at National University Singapore said: "I was stunned and impressed by the immensity of the landslide. Around me, there were gasps and oohs and aahs."
Asked if the area has since been closed off, the National Parks Board (NParks) said access to the viewing platform - which faces the cliff across the lake - will remain open, since the cliff itself is not linked to the viewing deck.
The authority will, however, evaluate the condition of the cliff.
Preliminary assessments do not show any signs of further soil movement, NParks said.
It added: "This rockslide incident could have been caused by overburdened soil at that section of the cliff and the continuous rain over the past few days.
"We will continue to monitor the stability of the cliff."
A previous source of granite, the Singapore Quarry is now a wildlife sanctuary.