Nearly two dozen countries next Wednesday will take part in a full-scale test of the Indian Ocean's tsunami alert system, using the 2004 Sumatra quake as the basis for the exercise, UNESCO said on Thursday.

Exercise IOWAVE 11 will re-enact the seismic events of December 26, 2004, simulating a 9.2-magnitude quake that occurs northwest of Sumatra, sending waves across the Indian Ocean that strike the coast of South Africa 12 hours later.

It will be a trial run for newly-launched Regional Tsunami Service Providers (RTSPs), located in Australia, India and Indonesia, which will issue simulated "alerts."

They are part of a region-wide tsunami warning and mitigation service, set up by 28 countries after the 2004 disaster, which claimed nearly a quarter of a million lives.

Until now, two bodies -- the Japan Meteorological Agency and the Pacific Tsunami Warning Centre -- have been in charge of tsunami alerts in the Indian Ocean.

They will end this interim job at the end of 2012, provided the handover goes well.

"The exercise aims to evaluate the system's operational capacity, the efficiency of communications among the different actors and the state of preparation of national emergency services," the UN's Educational, Scientific and Cultural Organisation (UNESCO) said in a press release here.

"The test will also include the evacuation of coastal communities in several countries, notably India and Malaysia."

So far, 23 countries have signed up for the October 12 test.

They are: Australia, Bangladesh, Comoros, East Timor, France (La Reunion), India, Indonesia, Iran, Kenya, Madagascar, Malaysia, Maldives, Mauritius, Mozambique, Myanmar, Oman, Pakistan, Seychelles, Singapore, Sri Lanka, Tanzania, Thailand, and Yemen

The Indian Ocean system was devised by the Intergovernmental Oceanographic Commission (IOC), a UNESCO body.