Divers say a towering coral known as the "Big Mushroom" at the heart of a world-famous dive site in Taiwan has been toppled after Typhoon Meranti struck last week.

The super-typhoon was the strongest storm for 21 years to strike Taiwan, leaving one dead before killing another 28 as it moved to eastern China. 

Green Island off Taiwan's east coast -- which attracts divers from around the globe -- has been left reeling from the underwater damage caused by the storm and by the smaller Typhoon Malakas which followed it. 

It was home to the 10-metre-high (33 feet) mushroom-shaped pore coral, the biggest of its kind in the world.

But videos posted by local dive instructor Yu Ming-hung show the coral lying on its side on the seabed.

He called it a "loss and heartache for the Taiwanese" on his Facebook page, where the footage was posted.

Green Island and the nearby Orchid Island remain largely cut off. Regular ferries have not yet resumed due to debris in the harbour. 

The storm also swept away a lighthouse at a dock in the eastern county of Taitung, where ferries to the islands depart. Tourists were evacuated from the islands before Meranti hit.  

Officials said they feared an increase in extreme weather could cause more damage to marine life and to tourism.

"We were shocked to hear the news. It is a great pity," said Chuang Hui-fang, a department chief at the East Coast National Scenic Area Administration, of the toppling of the "Big Mushroom". 

"The magnitude of typhoons is getting bigger than before. It seems these unusual weather phenomenon are becoming increasingly common."

The "Big Mushroom" is at least 1,000 years old and has grown on the 18-metre-deep seabed since the Song Dynasty, diver Yu said on his Facebook post. 

It has been named as one of the top 20 iconic dive sites in Asia by the Professional Association of Diving Instructors.