Emergency text messages could previously only be sent to a mobile phone's registered service address, meaning visitors to the area missed out.
The change allows a text message to be sent to mobile phones that are within the vicinity of an emergency.
Previously, Telstra was the only network able to send emergency text alerts. Optus and Vodafone Hutchison Australia networks can now do it, too.
The service is designed to reach active mobile phones roaming on Australian networks.
Victorian Police and Emergency Services Minister Kim Wells and federal Justice Minister Michael Keenan launched the enhancement to the emergency alert system in Melbourne on Tuesday.
The Victorian government warned users at the beginning of this year not to rely solely on an SMS alert to warn of an emergency situation.
The system was put into effect for the first time on Sunday, when the NSW fire service sent emergency warnings to more than 600 people.
Keenan said the new system will serve the nation well going into the summer bushfire season.
The addition of Vodafone and Optus means all Australians will be covered on their mobile and landlines, he said.
"We're very keen to make sure everybody understands this is not the only way they can receive information from the Australian government, but it's one more way they can receive information," Keenan said.
He said that 99 percent of Australians have mobile coverage, and the government is working on a program to eliminate black spots.
Wells praised the system as a world first, and said Victoria has led the way.
"We now have a very good system, but it's not the only system people need to rely on when the fire season comes," he said.
He said that people need to be alert and aware of what's happening around them.
The federal government invested AU$60 million toward the warning system, with Victoria contributing AU$8 million.