Police forces are among groups in the UK and Ireland now able to highlight critical information to their Twitter followers by marking an important tweet as an alert - a potentially "life-saving" development in social media, officials said.
When they want information to come to public attention quickly they can send a tweet to their Twitter followers - marked as an alert - which highlights the tweet with an orange bell for added visibility.
As well as the UK's 47 police forces, others signed up include the Environment Agency, An Garda Siochana, the London Fire Brigade, the Mayor of London's office, the Foreign Office and the Child Exploitation and Online Protection Centre.
Twitter users who sign up for an account's Twitter alerts will receive a notification directly to their phone via SMS. Users of Twitter for iPhone or Twitter for Android will also receive a push notification direct to their mobile.
While participating organisations choose what information merits being an alert, this feature is intended for crisis, disaster and emergency communications.
Commander David Martin, in charge of emergency planning for the Metropolitan Police Service, said: "Getting fast and accurate information to the public in a major incident or terrorist attack really could make a life-saving difference.
"Using social networking sites, including Twitter, gives us additional ways to talk directly to the public. Twitter alerts means that our messages will stand out when it most matters."
John Curtin, head of incident management at the Environment Agency, said the alerts system "allows us to lift up the really urgent life-threatening issues" out of all the information packed into people's Twitter feeds.
He said the process will be particularly useful "if there is an immediate risk to life".
Mr Curtin said it is important that the system is not overused as that would damage the impact it is intended to have.
He added: "Twitter don't want us to overuse it because you lose the value of it, so there will be some sort of judgement. People have to make judgements already in any sort of crisis management."
"We just want to make sure the impact is kept - that this is one of those really exceptional things that's happening, you need to pay attention now. If you overuse those types of things you get the cry wolf response."
Mr Curtin added: "Digital communications is enhancing the way we share warning information during an incident. During an incident such as flooding, we see significant spikes in related conversation.
"Twitter alerts provide an excellent opportunity to increase the visibility and urgency of our most vital warning messages so that people can take action to protect themselves and their property."
Twitter alerts, which comes to the UK and Ireland today, launched with a number of participating organisations in the US, Japan and Korea in September.
Since launching, the service has been used by international organisations to disseminate information during emergencies involving public safety, accessibility and bad weather.