As a follow-up to this answer which states that the “Z” trains from Beijing to Hong Kong and which take 24 hours are actually non-stop services (permitting immigration formalities to take place in Beijing), I wonder if there are any longer non-stop train services?
“Non-stop” here means actually no stops where you can get on or off the train, not just “direct”. Trains may have additional stops before or after the longest non-stop part of the journey.
"Longest" here means by time.
They should be scheduled passenger services.
If there are no longer such services, what's the next longest after this one?