Northern Territory police have arrested a man after a motorised bicycle chase through Darwin's CBD.

Police first spotted the motorised bicycle at 3:50am, when the 39-year-old rider ran a red light.

They chased the man down Mitchell Street, where he ran a second red light and sped away.

Watch Commander Gary Smith says the man - who had no helmet or front lights - reached speeds of 68.7 kilometres per hour.

"Just to add to our little case there, he had an electronic speedo which he had set, and it seemed to be timing his ride," he said.\

"The rider was eventually caught near the casino.

"[When we] asked him why he didn't stop he said to us [that] he was up for a chase."

Police are still deciding what to charges to lay.