G20 security command opens in Brisbane

The nerve centre of Australia's largest ever peacetime security operation has opened in Brisbane - six months ahead of the G20 leaders' summit.

ASIO, the Australian Federal Police and Defence are moving into Queensland police headquarter's new command centre, with high-tech CCTV monitoring, as part of a $97 million security program.

More than 5500 police officers, mainly from Queensland, will outnumber the 4000 visiting international officials.

The security is being intensified around the CBD and South Bank precinct for world leaders, including US President Barack Obama, Chinese counterpart Xi Jinping and Indonesia's next president in November.

"Operation Southern Cross will be the largest peacetime security operation in Australia's history," Queensland's deputy police commissioner Ross Barnett told reporters.

"We recognise the terrorist threat that currently exists in this country and we'll take all the necessary precautions."

But Assistant Commissioner Katarina Carroll says police will be engaging with protest groups and allowing peaceful demonstrations.

"However, if there is that certain line in the sand that is drawn and they step over that, there has to be action taken," she said.

"If there are groups that don't want to engage with us, we'll be out engaging with them."

While the 2007 APEC summit was criticised for shutting down too much of Sydney, Josh Frydenberg, the parliamentary secretary to the prime minister, said Brisbane would be showcased to the world.

"We're not seeking to lock down Brisbane," he said.

"I'm saying to those protesters: don't hijack our event."