Hong Kong billionaire Li Ka-shing's Cheung Kong Infrastructure Holdings Ltd has offered A$7.3 billion ($5.4 billion) in cash for Australia's Duet Group as it seeks to expand its power and gas pipeline assets.

CKI offered A$3 per share for the infrastructure company, 28 percent more than Friday's close, Sydney-based Duet said on Monday.

The company's board said it is evaluating the nonbinding and conditional offer that pushed its shares to the highest level in eight years.