Twitter is digging deeper and deeper into the fabric of our society — and not just our entertainment.

Today, the newsy up-to-the-minute social network launched Twitter Alerts, a public service that will allow “credible organizations” such as government agencies and NGOs to warn and alert the public during emergencies and natural disasters.

Initial participating organizations include the Red Cross, Center for Disease Control, Homeland Security, and many state and regional police departments.

“When news breaks about a weather or safety emergency, government agencies and emergency responders jump into action on the ground and on Twitter, delivering critical and timely information and engaging with constituents,” Twitter’s Bridget Coyne wrote in a blog post. “We saw this following Superstorm Sandy, the tsunami in Japan, and the manhunt in Boston.”

The alerts are sent out as push notifications, but Twitter users have to sign up to receive them on a page like this one:

Twitter Alerts

Once you sign up by clicking that long blue button, you’ll see a question like this one, asking to use your phone number:

Twitter alerts

The rationale is that now Twitter Alerts can use your mobile number to send SMS messages, which you are more likely to receive immediately — since not all Twitter app users on iPhone and Android have enabled push notifications. It’s not a follow, per se; it simply signs you up to receive alerts.

The feature seems to have been born out of the earthquake and tsunami disaster a year ago in Japan.

Then, Twitter launched Lifeline, which helped Twitter users in Japan find the best, most relevant information quickly. Twitter Alerts, however, will not require users to check Twitter; the messages will come to their phones.

This is a really, really interesting feature and a natural progression for Twitter that not only provides a great public service (great for us) but also embeds Twitter still deeper into the fabric of how hot news spreads (good for Twitter). It’s a great coup for the company on the eve of its IPO, and an excellent reason for non-Twitter users to sign up.

Not least, it’s also a great way for government to get the word out about immediate problems. Participating organizations include: