For the record, the govt. is perfectly correct here. This is safety information and there are time-tested methods of distributing public safety warnings. Methods that are work and are managed so that people don't get mixed/conflicting messages.
And increasingly, it's the Governments that are turning away from those time-tested methods.
These days, there's a big push to using the Internet. I say it has its place. Licensing of that data is a big issue, and it's an issue I face myself, as someone who provides emergency communications in such events.
Restrictive licensing prevents someone such as myself, sending a map of affected areas to a station in the area who is cut off from traditional network services. (i.e. via slow-scan television or packet radio instead of email or television) I suppose if taken literally, these licenses prevent me from telling someone: "Don't take some road, it's closed due to floods". This is not helpful.
Even if I was allowed to say what roads were closed or where the fire was located; by the time it has filtered through about 4 sets of ears, brains and mouths, who knows what will come out the other end? The old story of the military unit sending the message "Send re-inforcements, we're going to advance!" getting back to HQ as "Send three and four pence, we're going to a dance!", comes to mind.
Contrast this to say me, taking a screenshot of a webpage depicting the affected areas, a dump of a spreadsheet; transmitting that to someone out in the field and them printing off a few copies/relaying to others. They get a more-or-less verbatim copy of what was on the government authority's site.
The government need to decide if the public should have this information or not. If they're worried about it getting into the wrong hands, then they should keep it secret; and we'll collectively run around like headless chooks causing even more mayhem.
I say: let people re-broadcast the material. If presented to the public in any form, it will be rebroadcasted one way or the other, so it's pointless putting any means to stop it. Doing so does more harm than good.