The Hamas Al Qassam website has an interview with Akram Ahmed Salmi, a terrorist who was recently released after nine years in prison.
He claims that Hamas was manufacturing missiles in 2002 that were meant to be shot to the Knesset, to Ben Gurion Airport and "most importantly" to the settlement of Bet El.
Salmi claimed that the expertise to manufacture the rockets was transferred over from Gaza and that some 20 Qassam missiles had been built. The manufacturing slowed down a lot after Israel launched Operation Defensive Shield, as the priority then changed to building IEDs to attack the IDF troops.
According to Salmi, the entire factory went up in smoke in late March 2002 when a fire broke out, destroying all the rockets.
It is unclear how true this story is. The first Qassam launch from Gaza may have been in January 2002, with a known Qassam attack in the West Bank on February 13th.
According to this caption, a Qassam factory was discovered in Tulkarem on March 9, 2002.
I couldn't find any information about a fire in the West Bank in late March 2002. So this could all be some after-the fact bragging. But it is significant that there were some Qassams from the West Bank early in the intifada, and there was little at the time stopping it from escalating - except the fear that the IDF would go crazy if it happened.
And that is not a small thing.