Is there a high speed train from Hong Kong to Fuzhou? how long will it take?

No direct high speed train is available for this route. Anyway, transfer is needed if you wanna travel by rail. Take Hong Kong East Rail line at Hung Hom Station to Lok Ma Chaub in 40min. There you can go through the immigration to Futian Checkpoint metro station. At the station, take Longhua metro line to Shenzhen North Rail Station. There you can take a high speed train to FZ South in around 5.5h.