A Chinese investment company has bought two of the biggest watermelon farms in Australia's Northern Territory for AUD$27.5 million (US$20 million), in what is reported to be one of the most significant horticultural deals in the state's history.

ABC News reported the Hong Kong-based CK Hutchinson Holdings - which is owned by the autonomous territory's richest man, Li Ka-shing - bought Stuart and Kane Younghusband's melon farms near Mataranka, which cover a combined area of about 1,900 hectares.

The new owners have signed a 10-year lease with the New South Wales-based Rombola Family Farms, which was this year found to have sold rockmelons (cantaloupes) contaminated with listeria, which led to a miscarriage and the deaths of seven people.

ABC said it understands the Foreign Investment Review Board gave its approval for the sale to go ahead, which settled shortly before Treasurer Josh Frydenberg blocked one of CK Holding's subsidiaries, CK Investment, from buying the majority of Australia's gas transmission pipeline.

The two Mataranka farms, which were run as separate businesses, produced about 25,000 metric tons (MT) of watermelons every year, which is more than half of the Northern Territory's 46,000MT annual melon production.

Agricultural consultant Ian Baker reportedly said the sale of the two properties was one of the biggest horticultural deals he had seen in northern Australia.

"In the [Northern Territory] horticultural industry, farms have been selling between $5 [million] and $10 million, so this is a big sale," Baker was quoted as saying.