Two bystanders who were seriously injured in a knife attack at Amsterdam's Central Station are US citizens, the US ambassador said Saturday.

"We are aware that both victims were US citizens and have been in touch with them and their families," Pete Hoekstra said in a statement.

Police shot and wounded a 19-year-old Afghan man with a German residency permit. He stabbed the two people at the Dutch capital's busy station in the city centre on Friday.

"We are seriously taking into account that there was a terrorist motive," Amsterdam police spokesman Frans Zuiderhoek told AFP.

Earlier witnesses described scenes of panic as gunshots rang out and thousands of commuters and tourists were evacuated from the rail terminus shortly after midday on Friday.

"A man in the west side tunnel of Amsterdam Central Station stabbed two other people and directly after that he was shot by the police," another police spokesman Rob van der Veen said, adding terrorism was not being ruled out by investigators.