The mayor, 53, who was elected by the Socialist Party, was found dead at home.
A GNR source said Bernardes was found dead on a bed in his home in Turcifal, with stab wounds to the neck. A knife was also found next to the body.
When asked about possible signs of a crime in the house, the same source did not want to give further information.
The police source told Lusa that elements of the Homicide Investigation Brigade of the Lisbon Judiciary Police had gone to the scene to investigate the circumstances of the mayor's death.
In March, the political committee of Torres Vedras of the PS approved the re-candidacy of Carlos Bernardes to the presidency of the municipality, in the district of Lisbon, in the local elections this year.
"Within my availability, I continue to serve the party and my land", said the mayor at the time, promising a "work of continuity" and pointing out the priorities of the next mandate.
Carlos Bernardes first won the mayoral race in 2017 and was vice-president between 2005 and 2015.
In 2015, he took over as president when the then leader of the executive, Carlos Miguel, resigned to take up a position in the government.