Sri Lanka has shipped back to Britain container-loads of waste that the government said was brought into the island in violation of international laws governing the shipping of hazardous material.

The 21 containers -- holding up to 260 tonnes of rubbish -- first arrived by ship in the capital Colombo's main port between September 2017 and March 2018, customs told AFP, adding that they departed Sri Lanka on Saturday.

They were meant to carry used mattresses, carpets and rugs, but had also contained hospital waste, officials said.

"The shipper had agreed to take back these 21 containers," customs spokesman Sunil Jayaratne told AFP on Sunday.

"We are working to secure compensation from those responsible for getting the containers into the country."

Customs did not reveal the type of hospital waste, but previous illegally imported containers had included rags, bandages and body parts from mortuaries, according to officials.

Another 242 containers from Britain, which the government said was carrying illegal garbage in violation of international law, remains abandoned at the same port and at a free trade zone outside the capital.

They arrived in 2017 and 2018.

The government is currently engaged in legal action against the shipper to have the 242 containers removed from the country.

A Sri Lankan investigation last year into nearly 3,000 tonnes of illegally imported hazardous waste found the importer had reshipped about 180 tonnes to India and Dubai in 2017 and 2018.

Several Asian countries, sick of being the wealthy world's rubbish dump, have in the past two years turned back container-loads of waste from foreign shores.