The US Federal Aviation Administration (FAA) has registered 300,000 drone owners in the first month of opening the process for small unmanned aircraft used for recreational or hobby purposes.

The online registration, which began on 21 December, is applicable for drones that weigh between 250g and 25kg.

Registered owners receive a certificate and registration number, which needs to be displayed on all aircraft.

Owners who have registered their unmanned aircraft will be able to fly them outdoors. Registration is valid for three years.

A similar process for commercial use drones is expected to be undertaken by 21 March.

FAA administrator Michael Huerta said: "The registration numbers we are seeing so far are very encouraging.

"We are working hard to build on this early momentum and ensure everyone understands the registration requirement."

A registration fee of $5 was reimbursed to all owners who registered their drones in the first 30 days.

"We are working hard to build on this early momentum and ensure everyone understands the registration requirement."

US federal law requires aircraft registration to ensure safety of manned aircraft, and to be traceable in the event of any security breaches.

A taskforce comprising representatives from the unmanned aerial systems (UAS) and manned aviation industries, the federal government and other stakeholders was formed in October to make recommendations to the FAA over drone registrations.

The group will advise the Department of Transportation on which aircraft should be exempt from registration due to a low safety risk, including toys and certain other small UAS.

Transportation secretary Anthony Foxx said: "Registering unmanned aircraft will help build a culture of accountability and responsibility, especially with new users who have no experience operating in the US aviation system.

"It will help protect public safety in the air and on the ground."

Small unmanned aircraft pose new security and privacy challenges.

Pilot sightings of UAS doubled between 2014 and 2015. Reports ranged from incidents at major sporting events and flights near manned aircraft, to interference with wildfire operations, FAA said.

Huerta said: "These reports signal a troubling trend.

"Registration will help make sure that operators know the rules and remain accountable to the public for flying their unmanned aircraft responsibly.

"When they do not fly safely, they will know there will be consequences."

Image: AltiGator civil drone OnyxStar Fox-C8 XT. Photo: courtesy of ZullyC3P / Wikipedia.