A group of Federal MPs say they doubt Agriculture Minister Barnaby Joyce’s reliability, after his decision to oppose a Chinese-backed coal mine.

Mr Joyce’s stance defied the principle of “cabinet solidarity” and opposed the approval of the mine on prime agricultural land, reigniting debate within the Collation about whether he has the credentials to succeed Warren Truss as deputy PM and Nationals leader.

It has also been reported that the Chinese raised concerns at the highest levels of government about the possibility Mr Joyce would one day lead the junior Coalition partner.

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The ABC spoke to a number of Nationals MPs who said his behaviour had damaged his standing internally.

Liberals said it was further evidence he should not succeed Mr Truss.

“(It’s about) cabinet solidarity … at that level of the Government you have to play by the rules,” one Liberal told the ABC.

The senator said the Chinese spoke of their concerns about the possibility Mr Joyce following in the footsteps of Nationals leaders who had also taken on the trade portfolio.

“There was tremendous angst among the Chinese that he could become deputy prime minister and trade minister,” the senator told the ABC.

When asked if this was because Mr Joyce was seen as ‘xenophobic’, after Shenhua Watermark project manager Paul Jackson made the comment on Monday, the senator said, “exactly”.

But Nationals Senator Matt Canavan told ABC radio on Wednesday that “people like those with a backbone, and hate machiavellian people”.

Environment Minister Greg Hunt gave conditional approval to the $1 billion Shenhua Watermark project in northern NSW last week.

Since then, Mr Joyce argued strongly against it but said his concerns stemmed from his position as agriculture minister, not because the project was in his electorate.

Mr Joyce was at odds with the Prime Minister Tony Abbott about the issue, with the PM arguing it was possible for agriculture and mining to coexist on the land.

“My impression is Tony can’t stand the bloke,” a Lower House Liberal told the ABC.

“I think the PM is dreadfully worried about Barnaby as deputy PM because he’s a loose cannon.

“Tony has no problems leaving Warren in charge (as acting Prime Minister when he’s overseas) — I don’t think he’d say the same about Barnaby.”

A spokesman for the Prime Minister said Mr Abbott and Mr Joyce had an excellent working and personal relationship and to suggest otherwise was completely false.

– with AAP