Scientists fired the first beam of protons around a 27.36-kilometre tunnel on Wednesday in science's next great step to understand the makeup of the universe.

The Large Hadron Collider – built since 2003 at a cost of USD 3.8 billion – provides scientists with much greater power than ever before to smash the components of atoms in a bid to see how they are made.

"The beam is the size of a human hair," Paola Catapano, a spokeswoman for the host European Organisation for Nuclear Research said after the protons were fired into the accelerator below the Swiss-French border at 0732 GMT.

The organisation, known by its French acronym CERN, is firing the protons – a type of subatomic particle – around the tunnel in stages, several kilometres at a time.

Once the beam has successfully been tested in clockwise direction, CERN will send it counter clockwise. Eventually the two beams will be fired in opposite directions with the aim of smashing together protons to see how they are made.

The start up – eagerly awaited by 9,000 physicists around the world who will conduct experiments at CERN – overcomes the objections of some sceptics who fear the collisions of protons could eventually imperil the earth.

The sceptics theorise that a by-product of the collisions could be micro black holes, subatomic versions of collapsed stars whose gravity is so strong they can suck in planets and other stars.

"It's nonsense," said James Gillies, chief spokesman for CERN, before the experiment’ start.

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