There's silence from some National MPs as the Prime Minister faces a potential leadership showdown.

Chris Luxon's called an urgent Caucus meeting in Wellington tomorrow morning, after rumours emerged he doesn't have his party's full support.

He's touched down in Wellington, batting off questions and saying he'll talk to media tomorrow.

NZ Herald political editor Thomas Coughlan says MPs like Simeon Brown - who've previously stood behind Luxon - aren't returning texts.

"Usually, when there's a bit of speculation it's very easy, it takes two seconds to say - yes, I back the Prime Minister, and they do that all the time." 

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