At 4.55pm the city was hit by its biggest aftershock - a 5.4 magnitude shake centred about 10km southwest of Darfield at a depth of 10km - since the 4.35am shake which has left thousands without power and water as night falls. Since 4.30pm the city has experienced at least seven major aftershocks, including a 4.3 magnitude quake focused only 10km southwest of Christchurch at 6.54pm, according to the GeoNet website. By 10pm tonight there had been several further strong aftershocks.