One member of staff and a person from a partner company died in the crash.
The incident took place on Wednesday at about 17:20 local time, the firm said. The people who died were inside the vehicle as it fell from the building.
Nio says it immediately started an investigation into the incident in co-operation with government officials.
The third storey area from where the car fell has been variously described as a showroom, a testing facility or a car park.