Local fishermen rescued the girls, who jumped into the sea from the bridge at Veliyathura this afternoon, police said.
They have been admitted to the Thiruvananthapuram Medical College Hospital.
Their condition was stated to be stable by sources in the hospital.
The reason for their extreme step was under investigation.
Police said the girls were in a state of shock and have not yet been questioned.
Incidentally, the Class X state board examinations are now underway.