Katie Holmes just left the set of Jack and Jill at the Staples Center in downtown Los Angeles after receiving an emergency phone call this evening around 7:30pm PT.

The nature of the emergency is still unknown but a source tells us: "Her assistant answered Katie's cell and immediately tapped the director's assistant to have filming stopped. After a brief conversation, Katie left the set and her chauffeur picked her up and took her home. Everyone on the set was in shock because it was a key scene and now the production is on hold. No one is sure yet how this will affect the shooting schedule."

Tom Cruise is in Prague filming Mission Impossible IV so it seems likely something may have happened with Suri or another family member. It must be pretty serious to stop this multi-million dollar production.

More details coming ...