Despite the delays and technical glitches, UN's alarm mechanism rose to the occasion

'Everybody did exactly what they should have and the system worked very well.'

That was the reaction to the response by Patricio Bernal, executive secretary of Unesco's Intergovernmental Oceanographic Commission.

The UN's heritage body took the lead in developing an early-warning system after the 2004 tsunami, and it began operating 18 months later.

A total of 25 seismographic stations, three deep-ocean sensors, and a series of sea-level gauges instantly pick up signs of an earthquake.

The information is relayed in real time to the Japanese Meteorological Agency and the Pacific Tsunami Warning Centre in Hawaii.

They relay their analyses within minutes to focal points in the system's member countries, which then transmit the data to the national and local authorities responsible for emergency-response action.