Work is under way to prevent the slope responsible for Sunday's near-fatal landslip in Cheung Sha Wan from causing a disaster.
The Geotechnical Engineering Office said the overhanging slope was badly cracked and could produce a bigger slip in heavy rain.
Tonnes of rocks crashed on to Ching Cheung Road on Sunday, blocking it. The closure caused traffic chaos yesterday around Lai Chi Kok, Cheung Sha Wan and Shamshuipo and hit five bus routes.
The road may be closed for more than a week and 5,000 vehicles may have to use surrounding roads during peak hours.
Engineers said the landslide happened after repairs to two small slips which occurred there last month had been delayed by incessant rain. Senior geotechnical engineer Au-Yeung Yan-sang said the remaining slope was riddled with deep fissures or 'tension cracks' which could fill with rain water and cause a larger landslide.
'We are aware the closure is having a major impact on traffic but a larger failure may occur with more rain, so urgent, large-scale repair works will be required,' Mr Au-Yeung said.