Greek authorities say a strong earthquake with preliminary magnitude 5.5 has occurred off the southern island of Crete, but no damage or injuries have been reported.

Athens University's Geodynamic Institute says the undersea quake struck at 11:36 a.m. Wednesday, 30 kilometers (19 miles) south-southeast of Crete's southeastern tip.

Greece is one of the world's most seismically active countries, with hundreds of earthquakes recorded every year from several faults. But severe damage or injuries are rare.

In 1999, a strong earthquake near Athens killed 143 people, leveling some buildings and causing extensive damage to others.