"But if the shops actually knew that the pipes were not properly maintained and had not voiced their objection before, this could be a different story."

Kowloon Tong was hit particularly hard in the storm. At the popular Festival Walk, shoppers had to wade through ankle-deep water, according to photos mushrooming on social media.

About 10 shops and restaurants near the unwelcome "waterfall" were closed or partially shut to clean up the mess.

"Someone was suddenly screaming outside on Sunday night, so I went out and had a look," a manager at the Cole Haan boutique said.

"It was like it was raining inside the mall. I then found water dripping from the ceiling of my shop."

Half of the shoes and handbags in the boutique were soaked, he said.

An Estee Lauder booth directly below the food court came off worse. Its manager said: "All our products were soaked and can no longer be used."

Insurance-sector lawmaker Chan Kin-por said the mall looked set to face a huge loss, but expected it to be well covered by property insurance.

Watch: Hailstorm hits HK

But the chances of payouts for individual shops would depend on their tenancy terms, he added.

Structural engineer Dr Greg Wong Chak-yan said the cause of the leak would have a significant bearing on how the claims should proceed.

If the rooftop glass was broken, the mall owner and contractor must prove that the building's design and construction were up to standard, he said.