A tsunami has hit after an earthquake struck New Zealand's South Island. <br/><br/> The US Geological Survey said the magnitude-7.8 quake hit today, some 95 kilometre from Christchurch. <br/><br/> The tsunami arrived in the north-eastern coast about two hours later.<br/><br/> Officials said the first waves may not be the largest, with tsunami activity possible for several hours.<br/><br/> Residents were warned to head inland or for higher ground along the coast. According to Weatherwatch, a gauge at Kaikoura, 181 kilometre north of Christchurch, measured a wave of two metres (6ft 5ins).<br/><br/> Smaller waves are said to be arriving in Wellington and other areas. <br/><br/> Residents in the Chatham Islands, an archipelago 680 kilometre south-east of the mainland, were also being warned a wave would hit imminently by the civil defence.<br/><br/>Radio New Zealand reported thousands of people have already evacuated their homes. <br/><br/>Others have taken to social media to offer people a safe bed for the night.<br/><br/>