Complex sentence: The first person to reach the scene was a Greymouth police constable, who arrived on foot two hours after the accident--ambulances from Greymouth and Westport and helicopters from Christchurch arrived only later.
Split into simpler sentences: The first person to reach the scene was a Greymouth police constable, who arrived on foot two hours after the accident. Ambulances from Greymouth and Westport and helicopters from Christchurch arrived only later.