PARIS France, already on its highest security alert, is to boost security at airports around the capital and on trains after a wave of bomb hoaxes, the transport minister said on Sunday.

Security patrols at Paris airports will be increased by 40% and staff at the national railway company SNCF will be reinforced by 20% in addition to extra police patrolling railway stations, minister Clement Beaune said on France Inter.

France has been on its highest alert since Oct. 13 after a 20-year-old man fatally stabbed a teacher in the city of Arras in northern France.

"Transport (networks) have been places that have seen heavy tolls in attacks in the history of our country and in Europe," said Beaune.

Alongside the heightened risk, there were "people who are playing with fear", he said, referring to the wave of fake bomb alerts that have hit transport networks, schools and cultural centres over the last week.

Since last Wednesday, there have been 70 bomb hoaxes in airports in France, he said, adding that almost all of these alerts were sent from the same Swiss-based email address.

False alerts are generally punishable by two years in prison and a 30,000-euro fine. This can rise to three years in prison and a 45,000 euro fine if the alert includes a threat.

Beaune told France Inter that hoaxes are not "small jokes, they are serious crimes" and that they will be investigated.

The Palace of Versailles outside Paris was evacuated for security reasons at midday on Sunday for the seventh time in the last eight days, re-opening two hours later after checks were made, a spokesperson said.

(Reporting by Layli Foroudi; Editing by Nick Macfie)