NEW : Indonesian authorities issued the warning . Witnesses report only minor shaking on land . There were no immediate reports of damage , and hotel clerks contacted by CNN reported only mild shaking . The magnitude 7.3 earthquake was felt more than 250 km off Sumatra .
NEW : Indonesian authorities issued the warning . Witnesses report only minor shaking on land . The magnitude 7.3 earthquake was felt more than 250 km off Sumatra .