ASIO offers Manchester probe help

Australia's intelligence chief has offered Britain's MI5 support as investigations continue into the Manchester bombing.

ASIO boss Duncan Lewis told a Senate committee he and his officers had been horrified by the "act of cruelty and calculated, premeditated murder" which took the lives of 22 people outside a concert venue on Monday.

"Attacks such as this targeting some of society's most innocent causes my officers ... to redouble their focus and effort to counter this menacing threat," Mr Lewis said.

"I've contacted my counterpart, the director of MI5, to express our sympathy and offer support if required to our colleagues in the UK."

The advice to government was to keep Australia's national threat level at probable, where it has stood since September 2014.

"We remain vigilant in considering all of the intelligence information that might subsequently affect the national threat advisory system - the system is under constant and close review."

The travel advisory for Australians heading to the UK has been lifted to "high degree of caution".