Frisian Island authorities, which said the bag was found closed, identified the powder as “organic peroxide”, a highly flammable substance used in making plastics.
“A bag containing 25 kilogrammes of powder was found on the beach of Schiermonnikoog,” Jan-Willem Zwart, spokesman for the security services in the region, told AFP.
The Panama-registered MSC Zoe, which was mostly carrying toys, furniture and auto parts, lost the containers late on Tuesday while battling a storm off the Frisian Islands, an archipelago off the northwestern Dutch coast also
known as the Wadden Islands.
The MSC Zoe, which berthed at the northern German port of Bremerhaven late Wednesday, is one of the world's largest container vessels at 396 metres long and 59 metres wide. It was built in 2015.
Coastguards said three containers that had been transporting organic peroxide on the MSC Zoe have not been located and are thought to have sunk.
So far, around 20 containers have been located near the shores of these islands while another six were found in German waters.
Following appeals from officials in the affected islands, the Dutch ministry of defence announced soldiers would arrive Friday to help the clean-up operation on coastlines strewn with rubbish, notably polystyrene.
Volunteers have been helping collect items washed up on the beaches, which “look like a mess”, Zwart said.
Authorities have warned volunteers and locals not to touch any bags but to call police or the fire brigade.
“We strongly advise residents and people who have come to clean the beaches to… immediately seek medical attention if they come into contact with the bags (containing organic peroxide),” Zwart said, warning that the chemical substance “can cause burns”.
On the tiny island of Ameland “130,000 kg of debris has already been collected from eight km of beach”, the authorities said in a tweet.
On Ameland, the clean up is underway. Photo: DPA
In a statement shipping firm MSC Mediterranean Shipping said it took the incident “very seriously, both in terms of the impact of such accidents on the natural environment and in terms of any damage to customers' cargo”.
The firm said it had appointed a salvage company to help retrieve cargo and the clean-up and had deployed ships equipped with sonar after what it described as a “substantial spill of containers”.
Dutch broadcaster NOS on Wednesday broadcast footage of locals gathered around one of the containers, with toys and other materials strewn across the beach and one man carrying off a flat screen television.
It came after the first storm of the year, dubbed Zeetje, which caused severe weather along the North Sea coast, as well as further along at the Baltic Sea coast.
The storm caused flooding in some cities and towns in Germany, including Wismar, Lübeck and Flensburg.