The US-flagged ship 'Cape Ray' dropped anchor at the northern German port on Thursday evening and was immediately cordoned off.
It is carrying waste from the neutralization of tons of the deadly gas that was given up by the Syrian government in June and then rendered inactive at sea.
Port authorities described the load as "classic hazardous materials", and said standard additional security measures were in place for the unloading.
"This is a normal job for us," a spokesman for the BLG Logistics Group told Welt newspaper.
Once the unloading is complete, trucks will transport the waste by road to Munster to be disposed of.
Under intense international pressure, the Syrian government last year agreed to facilitate the destruction of its estimated 1,000 tonnes of chemical weapons.
A UN-sponsored mission oversaw the shipping of the country's last known stocks of sarin, mustard gas and VX nerve gas in June. The destruction of the most dangerous chemical weapons began at sea shortly afterwards.