OSLO—Two Norwegian companies are taking the lead in the race to build the world’s first crewless, autonomously operated ship, an advance that could mark a turning point in seaborne trade.

Dubbed by shipping executives the “Tesla of the Seas,” the Yara Birkeland now under development is scheduled in late 2018 to start sailing fertilizer 37 miles down a fiord from a production facility to the port of Larvik. Using the Global Positioning System, radar, cameras and sensors, the electric ship is designed to navigate itself around other boat traffic and to dock on its own.

The vessel will cost $25 million, about three times as much as a conventional container ship of its size, but its backers say without need for fuel or crew it promises to cut annual operating costs by up to 90%. The 100-container ship is scheduled to be in the water toward the end of next year, though initially it will be tested with a human at the controls.

The Birkeland is being jointly developed by agriculture firm Yara International ASA and Kongsberg Gruppen AS A, which builds guidance systems for civilian and military uses.

Petter Ostbo, Yara’s head of production who leads the project, said the company would look to invest in bigger ships and use them for longer routes once international regulations are in place for crewless vessels. “Maybe even move our fertilizer from Holland all the way to Brazil,” he said.

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The International Maritime Organization, which regulates maritime travel, doesn’t expect legislation governing crewless ships to be in place before 2020.

Shipping executives say autonomous vessels will be popular for short sea routes, but doubt they will replace oceangoing ships that move thousands of containers across continents with an average crew size of around 25.

“It’s not a matter of technology, which is already there, but a business case,” said Lars Jensen, chief executive of SeaIntelligence Consulting in Copenhagen. “Autonomous ships are expensive to begin with, and have to be built very robust, because if they break down, the cost of getting a team to fix them it in the middle of the ocean will be very high.”

In addition to reducing fuel and labor costs, the Birkeland project is being pitched as a way to cut emissions. The ship is expected to replace 40,000 truck drives a year through urban areas in southern Norway, the companies say.

Ship operators increasingly are being asked to introduce cleaner fuels when sailing close to populated coastal areas, especially in the U.S. and Europe.

“We want to go zero emission,” said Mr. Ostbo. “Even if some say climate change is not reality, it’s a business reality because clean sources of energy are more affordable than fossil fuels.”

The Birkeland will become autonomous in stages. At first, a single container will be used as a manned bridge on board. Then the bridge will be moved to shore and become a remote-operation center. The ship will eventually run fully on its own, under supervision from shore, in 2020.

“When the bridge goes on land, it will be something like flying a drone from a command center,” said Kongsberg’s chief executive, Geir Haoy. “It will be GPS navigation and lots of high-tech cameras to see what’s going around the ship.”

The Norwegians aren’t alone in looking into autonomous shipping. British manufacturer Rolls-Royce Holding PLC is investing in similar technology and plans to launch robotic ships by 2020. The first vessels will likely be tugboats and ferries, with cargo ships that can sail through international waters to follow.

“Once the regulation is in place, I can see this spreading fast,” Mr. Haoy said. “There is a lot of interest from operators of coastal tankers, fish-transport vessels and supply ships that are knocking on our door.”

Write to Costas Paris at costas.paris@wsj.com