A tree that fell on a bus on in Hong Kong during a storm and injured seven passengers was on private property and the land owner was responsible for its maintenance, the Development Bureau said on Tuesday.

The news came after the Hospital Authority said all the injured had been discharged.

The accident, which occurred on a main road on The Peak during a No 3 typhoon warning signal on Monday, happened just a month after a flame tree on a roadside crashed onto a school bus in Ho Man Tin, injuring three people.

But a bureau spokeswoman said that inquiries had established the fallen tree, which was on a slope next to The Peak police station, belonged to a private owner.

“After our extensive observation, we have reason to believe that the tree fell down due to the heavy wind on Monday night, although the owner should contact and arrange for qualified professionals to carry out inspections of the trees involved and nearby to ensure public safety,” she said.

Workers clean up after a tree crashed onto a double-decker bus, shattering its windscreen.

The three-metre (10 feet) tall tree, a persimmon-leaved litsea, fell onto the double-decker bus, a No 15 service operated by New World First Bus, travelling down Peak Road to Central at about 7.40pm on Monday.

The front of the bus and its windscreen was severely damaged and seven passengers suffered cuts from broken glass and other injuries.

Professor Jim Chi-yung, a tree and soil expert at the Education University of Hong Kong, said he suspected that decay of the tree’s trunk and branches had caused the collapse.

“Sound wood has long and strong fibres to impart considerable mechanical strength. It is very rare for a toppled tree to shatter into small pieces when it falls,” he said.

“If this is the case, it means that the fallen tree trunk and large branches have decayed badly.”

Jim added that the tree’s roots might also have suffered damage from slope stabilisation work, a technique where soil was compacted and covered with a layer of concrete.

“The slope condition has been rendered less suitable for tree survival. Soil degraded by compaction and sealing cannot allow normal root growth,” he said.

“Existing roots will decline and new roots will not be able to develop … which will lead to collapse as the continued decline of the root system weakens the tree’s anchorage.”

The accident happened as Typhoon Nesat skirted the city. The No 3 typhoon signal remained in force for around 28 hours, but the Observatory downgraded it to strong monsoon status at 3.40pm on Tuesday.

The No 3 signal is the fourth-highest storm warning under the city’s weather system, with sustained wind speeds of up to 62km/h (38mph) expected.

Private land owners are responsible for the management of trees on their property, but the city’s tree management policy was put under the spotlight in September after the 15-metre tall flame tree fell on the school bus.

Secretary for Development Bernadette Linn Hon-ho said after the incident a task force would be set up to look into three areas – whether current guidelines on tree inspections were enough, follow-ups on trees that needed attention and whether checks were adequate and regular enough.

She added that the authorities had also ordered the inspection of 10,000 roadside flame trees by the end of September.

The development chief said that the government also planned to examine all roadside trees, but inspections would have to be carried out in batches because of the large numbers involved.