A $13 billion bid by a Chinese and Hong-Kong-based consortium for the bulk of Australia's gas networks has been formally blocked by Treasurer Josh Frydenberg.

In June, CK Group launched the takeover bid for APA Group, which owns 15,000 kilometres of pipelines, or about 56 per cent of Australia's gas pipeline transmission system, including 74 per cent of New South Wales and Victorian pipelines.

Significant national security concerns about the sale were raised, and Mr Frydenberg foreshadowed earlier this month he would block the deal because it was not in the "national interest".

He has now confirmed that decision.

"I have formed this view on the basis that it would result in a single foreign company group having sole ownership and control over Australia's most significant gas-transmission business," Mr Frydenberg said.

"My decision is not an adverse reflection on CK Group or the individual companies. CK Group companies are already a substantial investor in Australia's gas and electricity sectors and a significant provider of infrastructure services that millions of Australians rely upon.

"The Australian Government welcomes CK Group's investments in Australia and its broader contribution to the Australian economy."

A map showing APA Group's gas assets across Australia. ( Supplied: APA Group )

Mr Frydenberg said the Government continued to welcome foreign investment into Australia that was not "contrary to our national interest".

It was understood CK Group would respond to the decision in a statement to the Hong Kong stock exchange on Wednesday.

The ABC contacted APA for comment.

CK Group was blocked from buying Ausgrid — the owner of the electricity poles and wires in NSW — two years ago over similar concerns.