The project is being developed at Google X, the company's clandestine tech research arm, which is also responsible for its self-driving car.
Project Wing has been running for two years, but was a secret until now.
Google said that its long-term goal was to develop drones that could be used for disaster relief by delivering aid to isolated areas.
They could be used after earthquakes, floods, or extreme weather events, the company suggested, to take small items such as medicines or batteries to people in areas that conventional vehicles cannot reach.
"Even just a few of these, being able to shuttle nearly continuously could service a very large number of people in an emergency situation," explained Astro Teller, Captain of Moonshots - Google X's name for big-thinking projects.
Australia tests
Google's self-flying vehicle project was first conceived of as a way to deliver defibrillator kits to people suspected of having heart attacks. The idea was that the drones would transport the equipment faster than an ambulance could.
"When you have a tool like this you can really allow the operators of those emergency services to add an entirely new dimension to the set of tools and solutions that they can think of," said Dave Voss, incoming leader of Project Wing
The prototype vehicles that the company has built have successfully been tested by delivering packages to remote farms in Queensland, Australia from neighbouring properties.
Australia was selected as a test site due to what Google calls "progressive" rules about the use of drones, which are more tightly controlled in other parts of the word.
Dual mode
Project Wing's aircraft have a wingspan of approximately 1.5m (4.9ft) and have four electrically-driven propellers.
The total weight, including the package to be delivered, is approximately 10kg (22lb). The aircraft itself accounts for the bulk of that at 8.5kg (18.7lb).
The small, white glossy machine has a "blended wing" design where the entire body of the aircraft provides lift.
The vehicle is known as a "tail sitter" - since it rests on the ground with its propellers pointed straight up, but then transitions into a horizontal flight pattern.
BBC's Nigel Cassidy reported on Amazon's drone project in December
This dual mode operation gives the self-flying vehicle some of the benefits of both planes and helicopters.
It can take off or land without a runway, and can hold its position hovering in one spot. It can also fly quickly and efficiently, allowing it to cover larger distances than the more traditional quadcopter vehicles available commercially.
The vehicles are pre-programmed with a destination, but then left to fly themselves there automatically.
This differs from many military drone aircraft, which are often remotely controlled by a pilot on the ground, sometimes on the other side of the world.
Eventually Google said it could use unmanned flying vehicles to deliver shopping items to consumers at home. That's a use that retail giant Amazon has already stated an interest in, with its proposed Prime Air service - the announcement of which generated headlines at the end of last year:
"The things we would do there are not unlike what is traditionally done in aerospace," said Mr Voss.
"It will be clear for us what level of redundancy we need in the controls and sensors, the computers that are onboard, and the motors, and how they are able to fail gracefully such that you don't have catastrophic problems occurring."
Other unusual vehicles have been investigated for humanitarian aid, including flying cars and hoverbikes, with the same aims of reaching cut-off areas quickly.
"We will have to see what kind of specific technology works best within the aid landscape, and if the new technology can integrate positively in the local context," said Lou Del Bello from news site SciDev.net, speaking about the category in general.
"It will need to demonstrate it can be cost effective, and respond to actual needs of local people."
