"Most of the trash we normally find is local Hong Kong trash," Stokes says. "But this is definitely coming from the mainland."

'Oil spill'

Residents from Hong Kong, Cheng Chau and Lantau islands have shared photos and videos showing trash strewn across beaches and floating in the water.

Stokes encouraged people to take photos, particularly of the labels and packaging.

"Trash talks, if you've got a load of mainland trash on the beach, how did it get there? (The government) can go to China and say this is a solid fact, we have a problem, we need your help to address it."

In a statement, Hong Kong's Environmental Protection Department said that "due to the effects of rainfall, marine currents and southwest monsoon wind, more marine refuse would be found during summer than other seasons."

The EPD estimates that the amount of waste being collected is six to 10 times that normally found on Hong Kong beaches in summer.

"We suspect that the floods in mid-June in (mainland China) might have brought the refuse to the sea and then the refuse is brought to Hong Kong by the southwest monsoon wind and the sea currents."

He added that coordinated government action on both sides of the border was needed to tackle the issue, and that while moves could be taken to catch the waste before it reached the beaches, trash on the sand is "a visual reminder for people that waste is a problem."

'Glacier of trash'

While much of the extra trash does appear to be of mainland Chinese origin, it is unclear just where it's come from. Stokes says that some could be being washed ashore by unusual tide or wind patterns that would usually flow out to sea.

"This could be putting the spotlight on a lot of illegal dumping that was already going on."

Images acquired by Sea Shepherd also suggested another source however: tiny Wai Ling Ding island.

The islands lies just south of Hong Kong, but is administratively part of China's Zhuhai municipality. Photos taken last week show a huge trash dump on the island, which Stokes believes is flowing into the sea and onto Hong Kong's beaches.

"It's pretty much like a glacier of trash that keeps sliding down the hill," he says.

'Not a serious problem'

District Councilor Zimmerman criticized the government for not taking action on marine waste, pointing out that the city had more than 3,000 open air refuse points that have "not kept up with the population size."

"Unless something is done, this is only going to increase, we're going to see more occurrences, especially during the rainy season," he said.

Mott McDonald, the company that produced the government report, did not respond to a request for comment.