OSLO, Feb 16 (Reuters) - Nel, a Norwegian maker of zero-emission hydrogen technology, said on Tuesday the authorities had fined two of its units a total of 25 million crowns ($2.97 million) for an incident at a hydrogen fuel station in 2019.

Hydrogen gas leaked from a tank at the station near Oslo in June 2019 and exploded, injuring three people when a pressure wave triggered airbags in their cars nearby, according to Nel and police reports.

"Nel conducted a thorough investigation of the incident in 2019 and has cooperated closely with the local authorities," Nel Chief Executive Jon Andre Loekke said in a statement.

"We're surprised by the conclusion and the size of the fines and will evaluate further potential actions," he said.

The fines were imposed on Nel subsidiary of Nel ASA and an unit partially owned by Nel, the company said.

The company has previously said it took responsibility for the incident, which it said was caused by an assembly error of a specific plug in a hydrogen tank in a high-pressure storage unit.

Since then, the company has changed assembly procedures and says its hydrogen refuelling stations are as safe as conventional fuelling stations.

Hydrogen, now mainly used in oil refining and to produce ammonia for fertilisers, is viewed as a potential green fuel. It can be made from water via electrolysis using renewable power, so-called green hydrogen, and only produces water when it burns. However, for now, green hydrogen is still costly to make.

($1 = 8.4276 Norwegian crowns) (Reporting by Nerijus Adomaitis; Editing by Edmund Blair)