At least six people were killed when a 6.3-magnitude earthquake struck the lower Himalayan region early Wednesday, leading to tremors rippling across north India and parts of Nepal and jolting people out of their sleep in scores of cities and villages.The National Centre for Seismology NCS said the epicentre of the 6.3-magnitude earthquake, which struck at 1.57 am, was in Nepal, about 90 km east-southeast of Pithoragarh.