British and Dutch Citizens obtaining Chinese visa en route in Asia

So me (British) and my Dutch friend are travelling to China at the end of our south east asia travels. We would be in Thailand when we would need to apply. So can we just go to the nearest Chinese consulate Embassy in Bangkok and apply for the entry permit there even if we are not nationals of that country? Will we need to send our passports anywhere? Can this be done (if we have all appropriate travel documents) in a day? Or could I apply 3/4 months before we travel to China when we are in England if we have our flights etc already booked? Thanks, from a panicked traveller.