Scientists have hailed a "new era" in their quest to unravel more mysteries of the universe as the world's biggest particle smasher started experiments with nearly doubled energy levels in a key breakthrough.

The tests at the European Organisation for Nuclear Research (CERN) came after a sweeping two-year revamp of the Large Hadron Collider (LHC).

They will help scientists study fundamental particles, the building blocks of all matter, and the forces that control them.

During its next run, researchers will look for evidence of "new physics" and probe supersymmetry, a theoretical concept informally dubbed Susy.

They will also seek explanations for enigmatic dark matter and look for signs of extra dimensions.

The new collisions of 13 teraelectonvolts (TeV) followed a muscling of the LHC, used in 2012 to prove the existence of the Higgs boson, which confers mass and is also known as the God particle.

CERN said everything went according to plan at the giant lab, a 27-kilometre ring-shaped tunnel straddling the French-Swiss border.

During what it dubbed as its season two, the LHC will in the course of the next three years strive to fill gaps in the so-called Standard Model, the mainstream theory of how the visible universe was created but which does not explain dark matter.

"It is time for new physics," declared CERN's outgoing director general Rolf Heuer.

"We have seen the first data beginning to flow. Let's see what they will reveal to us about how our universe works.

"It's not going to happen tomorrow, be patient," he added, as scientists monitoring the event broke into sustained applause and uncorked champagne.

On May 20, the LHC broke the record for energy levels colliding protons at 13 TeV — or 99.9 per cent of the speed of light — for the first time.

The LHC's previous highest energy for collisions was eight TeV, reached in 2012 before it closed for the upgrade.

Scientists set on unlocking more of nature's secrets

"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," Tiziano Camporesi, a spokesman for the project, said.

The LHC was used to prove the existence of the Higgs boson, a discovery that earned the 2013 Nobel physics prize for two of the scientists who had theorised its existence in 1964.

Scientists say the collisions now possible at CERN mark a 'new era'. ( AFP: Fabrice Coffrini )

The LHC allows beams containing billions of protons to shoot through the massive collider in opposite directions.

Powerful magnets bend the beams so they collide at points around the track where four laboratories have batteries of sensors to monitor the smash ups.

The sub-atomic rubble is then scrutinised for novel particles and the forces that hold them together.

One teraelectronvolt is roughly equivalent to the energy of motion of a flying mosquito, CERN says on its website.

But within the LHC, the energy is squeezed into an extremely small space — about a million, million times smaller than a mosquito.

It is this intensity which causes the particles to be smashed apart.

As part of the two-year recommissioning process, LHC engineers successfully introduced two proton beams, the source material for sub-atomic smash ups.

With the upgrade, the LHC can potentially be cranked up to a maximum 14 TeV.

AFP