NDWC hydrologist Jumleang Chutab said the towers had been regularly tested since their construction, but only on a "silent" basis.

Under the new testing, the speakers will sound daily in order to ensure they are functioning properly.

The speakers will not sound at full volume, nor will they emit siren sound or voice messages to be played during a real emergency, she said.

Aroon Kerdsom, chief of the Phuket Provincial Office for Disaster Prevention and Mitigation, said the audio testing would consist of little more than amplifying the sound of a "knock on a microphone".

The sound, expected to last just a few minutes, will only be audible within a radius of about 50 to 70 metres.

Smith Dhammasaroj, director of the NDWC, asked people not to panic when they heard the tests.

The tests are being conducted to increase public confidence in the system set up by the NDWC, which has faced criticism from some parties for not conducting regular audible testing of its towers.

The NDWC plans to arrange a large-scale system test and evacuation drill in about three months, said Aroon.

The first three towers installed in Patong have not been audibly tested since they were modified last year to adapt to the satellite technology used by the Thai-American consortium that won the government bid to install 62 towers in the region.