A US Navy helicopter lifted 20 aid workers off a stricken Taiwanese fishing vessel that had hit a reef while carrying out relief work for tsunami victims in the Solomon Islands, a Taiwanese official said Friday. The accident came as the Solomon Islands declared April 23 a national day of mourning for the 43 people killed when an 8.1 magnitude earthquake triggered a tsunami that crashed through coastal villages earlier this month. Another 7,000 people have been left homeless. The Taiwanese vessel had been returning to the western town of Gizo after delivering aid supplies to outlying islands when it struck a reef, Taiwan's Ambassador to the Solomon Islands, George Chan, said. Chan said the reef may have been uncharted or a new obstacle thrown up by the April 2 quake.