Stop press

"Stop Press" or "Stop the presses" is an idiomatic exclamation when significant information is discovered.

High-volume newspaper printing press.

The phrase stems from the printed news media industry. If the content of an issue needed to be revised just before, or during its printing the printing press was stopped and content amended, such as by changing the plates or type, before restarting it. Reasons to stop the press might be to add a news item or correct an error. This could cause delay and expense, such as by necessitating that already printed copies be discarded, so was generally reserved for highly significant content changes such as the breaking of a very important news story.