Starting on December 31, two F-18 fighter jets will be operational 24/7 to protect the airspace over the small, landlocked country, the armed forces said in a statement.

"From now on, the air police service will be on call 24 hours a day to guarantee the security and the sovereignty over Swiss airspace," the statement said.

The plan to increase Swiss airspace surveillance was proposed to parliament in 2009, but it was boosted by an incident five years later that cast a spotlight on the lack of round-the-clock protection.

In February 2014, an Ethiopian Airlines co-pilot, Hailemedehin Abera Tagegn, hijacked his own plane, carrying 202 passengers and crew from Addis Ababa to Rome, and forced it to land in Geneva.

When Tagegn locked himself in the cockpit while the pilot went to the bathroom, Italian and French fighter jets were scrambled to escort the plane through their respective airspaces.

But although the co-pilot-turned-hijacker quickly announced he wanted to land the plane in Switzerland, where he later said he aimed to seek asylum, Switzerland's fleet of F-18s and F-5 Tigers remained on the ground.

The Swiss airforce explained at the time that this was because its planes were only available during office hours.

Following the embarrassing incident, the Swiss parliament set a plan in motion to gradually scale up the airspace protection, with the aim of eventually ensuring that two fighter jets be constantly on call and capable of taking off with 15 minutes' notice.

The plan "has successfully been completed within the expected timeframe," Tuesday's statement said.

To finalise the project, nearly 100 additional jobs have been created across the airforce, army logistics and command centres, it said.

The new system will cost an additional 30 million Swiss francs ($34 million, 28 million euros) a year, it added.