The calculated distance (air line) between Tuen Mun San Hui and Kowloon is approximately 14 miles respectively 23 kilometers.
By car or train, the actual journey to Kowloon is certainly longer, as only the direct route (as the crow flies) between Tuen Mun San Hui and Kowloon has been calculated here.
Air line (approximately)
23 kilometers
13 nautical miles