US President Donald Trump and North Korean leader Kim Jong-un have arrived in Singapore for their historic summit.br br Mr Trump flew in aboard Air Force One, a few hours after Mr Kim touched down with his entourage.br br Their meeting - the first between a leader from the North and a sitting US president - will take place on Tuesday on the resort island of Sentosa.br br Mr Trump described it as a "one-time shot" at peace and said the two were in "unknown territory".br br The US hopes the summit will kick-start a process that eventually sees Mr Kim give up nuclear weapons.