GENEVA - Physicists have observed a new particle consistent with the long-sought Higgs boson, a theorised sub-atomic particle believed to confer mass, the European Organization for Nuclear Research (CERN) announced on Wednesday.

Two independent teams, ATLAS and CMS experiments, observed a new particle in the mass region around 125-126 GeV, at the level of 5 sigma certainty, the usual particle physics threshold for discovery, according to CERN.

"We've discovered a new particle of boson, possibly a Higgs boson, but we have to find out what kind of Higgs boson it is," Rolf Heuer, director of CERN told reporters.

Asked whether they found the last-missing ingredient in the standard model of physics, Heuer answered, "As a layman, I think we have it. But as a scientist, I have to say, 'What do we have?'"

He said the discovery opens the way to more detailed studies, requiring larger statistics, which will pin down the new particle's properties.

More data are needed to establish whether this new particle has all the properties of the Standard Model Higgs boson or whether some do not match, implying new physics beyond the standard model.

"We have reached a milestone in our understanding of nature," Heuer said.

CMS experiment spokesman Joe Incandela said: "We know it must be a boson and it's the heaviest boson ever found."

The results presented on Wednesday are based on data collected in 2011 and 2012, with the 2012 data still under analysis.

A more complete picture of current observations will emerge later this year after the Large Hadron Collider (LHC) provides more date, CERN said.

The reports from the two teams at the seminar got long applause from the audience.

Peter Higgs, a Scottish physicist who proposed the existence of such a particle in 1964, was present at Wednesday's seminar and press conference. He congratulated the scientists, calling it "an occasion for celebration."

"For me, it is really an incredible thing that's happened in my lifetime," Higgs said.

Higgs boson is part of a theory called "Higgs mechanism," an essential part of the standard model.

The mechanism, proposed by Higgs and other physicists in the 1960s, explains how elementary particles obtain mass. The particles gain mass by interacting with the Higgs field that exists everywhere in the universe.

As particles zoom around in this field, they interact with and attract Higgs bosons, which cluster around the particles in varying numbers. Certain particles will attract larger clusters of Higgs bosons, and the more Higgs bosons a particle attracts, the greater its mass will be.

Scientists have spent decades tracing down the Higgs boson, often nicknamed "God particle", which is believed to decay almost instantly after it interacts with other particles.

Besides diligent work of some 5,000 scientists from the two teams, the LHC operated by CERN also made great contributions to the achievement.

Housed in a 27-km circular tunnel at the Swiss-French border near Geneva, the world's largest atom smasher was first launched on September 10, 2008, but suffered a serious malfunction nine days later. It then restarted in November 2009.

CERN raised the energy level of the smasher to a new world record of 8 TeV in this April, which was believed to have greater potential in helping find new particles.

No matter whether Wednesday's observation draws scientists nearer to the end of the search for the elusive Higgs boson, physicists are excited for the prospects the discovery opens.

Heuer said scientists now know which direction to go for the future. "It's the beginning of a long journey to investigate all the properties of this interesting particle," he said.