TAINAN, Taiwan — Rescuers today found signs of life within the remains of a high-rise residential building that collapsed in a powerful, shallow earthquake in southern Taiwan that killed at least 18 people and injured hundreds. The emergency center in Tainan, the worst-hit city, estimated that 132 people were still missing more than 24 hours after the magnitude-6.4 quake struck at dawn Saturday. Tainan Mayor Lai Ching-te said in TV interviews from the site of the building collapse that life detecting equipment had found signs of life from at least 29 trapped people. Rescuers had already pulled out at least 247 survivors from the collapsed building.