The Large Hadron Collider (LHC) has started delivering physics data as a result of what has been described as a "milestone" collision.

After an almost two-year shutdown and several months of recommissioning, the world's largest particle accelerator is now providing collisions to all of its experiments at the unprecedented energy 13 tera-electronvolts (TeV).

That is almost double the collision energy of its first run.

The latest collisions mark the start of season two at Cern's LHC, opening the way to new discoveries.

The LHC is now expected to run around the clock for the next three years.

Speaking after stable beams were declared, Cern's director-general Rolf Heuer said: "Congratulations to everybody, here and outside! We should remember this was two years of teamwork. A fantasic achievement. I am touched. I hope you are also touched.

"Thanks to everybody. And now time for new physics. Great work."

But he reminded his colleagues they would have to wait for results, saying: "We have provided the basis, now the experiments have to follow.

"However, don't expect that it will be tomorrow, do not expect that it will be in a month - be patient."

During the first run of the LHC, the Atlas and CMS experiments announced the discovery of the so-called Higgs boson, an elementary particle that gives other particles mass, which had eluded detection for nearly 50 years.

It was the last piece of the puzzle known as the Standard Model.

With the ability to tap into higher energy, the scientists hope to explore mysterious realms of ''new physics'' that could yield evidence of hidden extra dimensions and dark matter.

Dark matter is the invisible, undetectable ''stuff'' that makes up 84% of material in the universe and binds galaxies together, yet whose nature is unknown.

As well as searching for dark matter, LHC scientists hope to create more and possibly different strains of Higgs boson, investigate anti-matter, and test the theory of ''supersymmetry'' which predicts that every known particle has a more massive hidden partner.

Supersymmetry seeks to fill gaps in the Standard Model, the all-encompassing blueprint of particles and forces in the universe that has been in place since the 1970s.

Protons race around the LHC beam tunnels at three metres per second below the speed of light.

The energy released when they collide is used to spark the creation of new particles.

"The collisions we are seeing today indicate that the work we have done in the past two years to prepare and improve our detector has been successful and marks the beginning of a new era of exploration of the secrets of nature," said CMS spokesman Tiziano Camporesi.

The £3.74 billion LHC, the most powerful atom-smasher ever built, was restarted in April after a two-year upgrade.

Last month scientists from the European Organisation for Nuclear Research (Cern) achieved test collisions between protons - the ''hearts'' of atoms - at 13 TeV for the first time.

Two beams of particles travelling a whisker below the speed of light are sent flying in opposite directions through 26.9km (16.7 miles) of circular tunnels beneath the Swiss-French border.

But the beam energy has only now been ramped up to its operating level of 13 TeV, almost twice the power used to uncover the Higgs boson two years ago.

Albert Einstein's famous equation E=MC2 showed that energy and mass are interchangeable. Upping the energy levels at the LHC increases the chances of some of it being converted to previously undetected, heavier particles - possibly including dark matter.

Over the two-year shut down, the four large experiments Alice, Atlas, CMS and LHCb also underwent a programme of maintenance and improvements.