The US government has granted six movie and television production companies permission to use drones for filming.

The decision by the Federal Aviation Administration marks an important step towards greater use of the technology by commercial operators, which is expected to generate billions of dollars in economic activity. It is only the second time such permission has been granted.

But there are restrictions on the permission, including that drones can only be used to shoot scenes in closed sets.

The companies were granted exceptions to certain regulations covering "general flight rules, pilot certificate requirements, manuals, maintenance and equipment mandates."

The FAA explains that the applications said that the drone operators for the production companies "will hold private pilot certificates, keep the UAS [unmanned aircraft systems] within line of sight at all times and restrict flights to the 'sterile area' on the set." The companies had to show the use of drones would not adversely affect safety on set.

The exemption requests were facilitated by the Motion Picture Association of America (MPAA).

Earlier this year, the FAA granted permission to BP and drone manufacturer AeroVironment to carry out aerial surveys over Alaska - the first commercial drone use approved by the organisation. 

Companies such as Amazon are developing drone systems. Use of unmanned aerial vehicles is likely to become a lucrative commercial area in the coming years, although regulations remain strict.