I would appreciate some help with a simple expression.

Here is a sample piece of text I want to search through.
Line one.
Line two: continued on.
Line three.

Line four: and now we continue.
Line five.

I want to find everything from the start of a line to a : The expression should select. Line two: Line four:

Can someone please help me build this? I currently have ^[^:]+: but this is not working as it is finding everything up to and including the first :.

Thanks for any help!