Physicists Francois Englert of Belgium and Peter Higgs of Britain have won the 2013 Nobel Prize in physics.

The Royal Swedish Academy of Sciences cited the two scientists for the "theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles."

The physics prize announcement was delayed by one hour, which is highly unusual. The academy gave no immediate reason, other than saying on Twitter that it was "still in session" at the original announcement time.

The academy decides the winners in a majority vote on the day of the announcement.