Jakarta, Mar 4 (IANS): Indonesian authorities have admitted that most buoys which were installed for tsunami alerts were not working when recently a 7.9-magnitude earthquake struck off Sumatra island, the National Disaster Mitigation Agency said on Friday.

"The damaged early warning systems will be repaired and those which are broken will be replaced by new ones," said Willem Rampangilei, agency head.

The earthquake on Wednesday, was first reported to have struck at a shallow depth of 10 km and had its epicentre west of the Sumatra island, EFE news reported.

The United States Geological Service (USGS) later corrected the depth to 24 km.

After the earthquake, the Indonesian meteorological agency issued a tsunami warning for the island, a common procedure for all earthquakes above 6.5 magnitude.

However, most tsunami warning buoys, which measure the force and speed of water movement, did not work and remain inoperative.

This circumstance delayed the lifting of the tsunami warning, officials said.

The earthquake caused no fatalities or major damage and no giant waves were recorded.