Rescue vessels are searching for survivors in the area where the accident happened, German authorities say.
Two other crew members were rescued after the collision early on Tuesday, German Sea Rescue Society (DGzRS) spokesperson Christian Stipeldey said.
The accident happened about 22km (13 miles) southwest of the island of Helgoland and 31km (19 miles) northeast of the island of Langeoog, the German Central Command for Maritime Emergencies (CCME) said in a statement.
Several ships are currently involved in a rescue operation in the area, the agency said.
“The emergency services are doing everything they can to rescue the missing people,” German Transport Minister Volker Wissing said in a statement.
“My thoughts are with the crew members, their relatives and the rescue teams who have been in action since early this morning.”
The ship, Verity, was sailing under a British flag and was on its way from Bremen in Germany to the British town of Immingham.
The other ship, Polesie, was under a Bahamas flag and travelling from Germany’s Hamburg to La Coruna in Spain.
Polsteam crew in good condition
The Verity, owned by the British company Faversham, was the smaller vessel with a length of 91 metres (about 300 feet), compared with the 190-metre-long (623 feet) Polesie – owned by the Polish shipping company Polsteam.
Krzysztof Gogol, a spokesperson for Polsteam, confirmed there were 22 crew members on board and said they were uninjured and in “good physical condition”.
Shortly after the collision, the Polesie stopped and took part in the search and rescue operation, Gogol said.
Rescue cruisers, an emergency tug, a pilot boat, a police patrol boat and a helicopter are helping with the search, according to the CCME.
A P&O cruise ship that was in the area, the IONA, has also been involved, the CCME added.
“On board the IONA, people can also receive medical care; there are doctors on board,” it said.
The search was taking place in difficult weather conditions, with strong winds and waves reaching as high as 3 metres (10 feet), the agency said.