Taipei  -  A 20-member Taiwan rescue team headed Friday to China to join Chinese rescuers in looking for survivors of an earthquake in which 21,500 people have so far been confirmed dead.

"All of our team members, who have various international rescue experiences, are anxious to join the mainland rescuers to find as many survivors as possible," Ou Chin-der, leader of the team and former deputy mayor of Taipei, said before departure to the south-western province of Sichuan.

Taiwan's Mandarin Airlines, which took the team to the provincial capital of Chengdu, was expected to transport back home about 100 Taiwan tourists stranded at Chengdu's airport, airlines officials said. About 1,000 Taiwanese are stranded in Sichuan in the wake of Monday's quake.

Bill Chang, director of the Civil Aeronautics Administration, said three other airlines would each dispatch a flight to Sichuan later Friday to take tourists home.

Fourteen Taiwan tourists are missing in the quake. Their bus was located via satellite images at a spot 10 kilometres from the epicentre in Wenchuan county, but the whereabouts of the passengers were unknown, officials at Taiwan's Travel Agent Association said.

Earlier, Taiwan media reported that a Taiwan satellite recorded a sharp drop in ionospheric density above Sichuan before the earthquake, verifying previous measurements that seismic activity affects ionospheric density and giving hope that one day earthquakes might be predictable.

Taiwan's Formosa-3 satellite was measuring the number of charged particles in the ionosphere, the uppermost part of the atmosphere, above Sichuan before the quake. It found that on the eve of the quake, the number of such particles dropped by half to 600,000 in the atmosphere about 1,000 square kilometres around Wenchuan, the quake's epicentre, the China Times said

Since then, Formosa-3, which was launched by the Taiwan National Space Organization in 2006, has recorded ionospheric density after 63 earthquakes measuring magnitude-5 or above, revealing a sharp drop in ionosphere density in 70 per cent of these cases. (dpa)