Van der Veen said the knifeman's condition was not life-threatening.
Pete Hoekstra, the USA ambassador to the Netherlands, said Saturday that the injured Americans were tourists visiting the city.
Around 250,000 people travel through Central Station every day, according to statistics provided by the Amsterdam.info online travel guide.
Initially, police said that the station - located in the Dutch capital's historic canal-ringed city centre - had been evacuated and closed off to all rail traffic.
Police said two train platforms were closed, but the station wasn't evacuated. Authorities said they were unable to provide any details about the motive for the stabbing, but that terrorism could not been ruled out.
Multiple police vehicles and ambulances were seen outside the large red-brick station, while red and white police tape cordoned off an area.
Police tweeted Friday that two people were injured in the stabbing.
A passerby's dramatic photo showed two police officers pointing guns at a man in blue jeans and sneakers lying on the ground inside a train station tunnel.
Hours after the incident, police said they were still investigating a possible motive for the attack and weren't excluding any possible scenarios. He said the violence happened shortly after noon when a man walked into a group of people. Friday is even handed one of the significant busiest days of the week, with many vacationers arriving for the weekend.
USA ambassador Pete Hoekstra earlier confirmed that both the victims, who were rushed to hospital after Friday's attack, were American citizens.