Li Ka-shing's Cheung Kong Infrastructure on Monday offered Aus$7.3 billion (US$5.4 billion) for an Australian energy group, just months after his bid for the country's largest electricity network was blocked on security grounds.

The Hong Kong billionaire's unsolicited and conditional Aus$3 per share offer for the Duet Group, an energy utility asset owner, represented a near-28 percent premium on its closing share price on Friday.

The move sent the stock more than 16 percent higher to Aus$2.73 in late afternoon trade Monday, although there was no certainty the approach would go any further.

"The boards of the Duet Group are currently evaluating the proposal and at this time security holders are advised to take no action as there is currently no certainty the proposal will proceed further," the target company said in a statement.

The Australian newspaper said China's State Grid and Singapore Power were believed to be working on a counter offer for Duet, which if true could spark a bidding war.

Duet owns electricity and gas networks in Victoria state as well as Western Australia's main gas transmission line.

The bid is Li's latest attempt this year to bolster his Australian business after suffering a blow when a proposal to buy the country's largest electricity network, AusGrid, was halted by the federal government in August.

Canberra rejected the move on national security grounds after introducing tougher rules for the sale of major Australian state-owned infrastructure to private foreign investors.

Chinese government-owned State Grid Corporation was also rejected, with reports at the time suggesting Canberra was concerned about Li's links to senior government officials in China.

Analysts believe approval for the new deal from the Foreign Investment Review Board (FIRB), could again prove troublesome amid heightened public debate about strategic assets falling into overseas hands.

"While we see Duet's assets as potentially less concerning from a national security perspective than Ausgrid, we believe FIRB approvals remain a significant barrier to a deal proceeding," RBC Capital Markets analyst Paul Johnston said in a client note.

The diversified Cheung Kong Infrastructure already has significant investments in Australia's energy sector, including in electricity networks in Victoria and South Australia.

The Hong Kong-listed company is a global player in infrastructure, with operations in China, Britain, the Netherlands, Portugal, New Zealand and Canada.

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