Hong Kong's leader on Sunday blamed a huge rise in rubbish blighting the city's beaches on refuse washed ashore from the mainland, and pledged talks with Chinese authorities to stem the tide.

Environmentalists have posted images on social media of trash covering several beaches, including plastic bottles and packaging with labels written in simplified Chinese characters -- used in mainland China but not Hong Kong.

Speaking after a visit to a coastal area Sunday morning, Leung Chun-ying said the refuse had been washed up in the city after heavy rain and floods struck southern China.

"A lot of domestic garbage was washed towards Hong Kong from the mainland... predictably due to heavy rainfalls and floods in the past few weeks," he told reporters on Lantau Island.

The extra waste put an increased burden on cleanup crews, he added, with the amount collected on beaches and other coastal areas "multiple times" what was seen over the same period last year.

"This is an extraordinary situation... we will follow this up with Guangdong relevant authorities," he said referring to the mainland province neighbouring the city.

Flooding is common during the summer monsoon season in southern China, but rainfall has been particularly heavy this year and many areas have been lashed by torrential rains this week.

"If you actually look at the trash... it does not look like stuff you find in supermarkets here... this is not like our normally trashed beaches," Hong Kong-based green activist Gary Stokes, of Sea Shepherd Conservation Society, said on Facebook.

But he added it is not "a chance to bash China", as the city should also tackle its own waste problems.

"Hong Kong creates more trash per capita than anywhere on earth, our track record on recycling efforts and cleanliness are dire," he said.

Domestic waste is deposited in landfill sites but also litters country parks, coastal areas and waterways.