Liz Truss spoke with Australian PM Anthony Albanese and New Zealand's premier Jacinda Ardern at the government's Chevening country residence on Saturday.
The meetings were being framed by No 10 as chats, rather than formal bilateral sessions, with politics likely to feature.
In advance of her talks with Ms Truss, Ms Ardern said the Queen's death and new King would be the "focus of conversation", with the pair also likely to discuss Ukraine and the UK's free trade agreement with New Zealand.
It was thought the meeting between Ms Truss and Mr Albanese may also touch on trade, with the countries last year signing a deal estimated by the government to be worth 2.3 billion pounds to the UK economy.
When his British counterpart won the Tory leadership contest earlier this month, the Australian PM tweeted: "I look forward to a continued constructive relationship and friendship between our nations and people."
Mr Albanese also signed the condolence book at Lancaster House with his partner, Jodie Haydon, during his visit.
He tweeted: "Today Jodie and I signed the condolence book at Lancaster House.
"In this time of great grief, we are thankful to be here paying our respects to the Queen for her services to duty, faith, family and the Commonwealth."
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