National leader Simon Bridges has attacked a "bungling, incompetent" Government over the early release of sensitive Budget details - and says claims the documents were hacked is a lie.

Bridges insisted to reporters this morning that the party's information about Budget 2019 did not come from hacking or any illegal activity.

And he has lashed out at Finance Minister Grant Robertson, saying he is "lying" for implying that National's information had come from hacking and being undemocratic by asking National not to release any more Budget material.

Yesterday National released Budget 2019 information throughout the day, forcing the Government onto the defensive.

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Treasury Secretary Gabriel Makhlouf said last night that the Treasury website had been hacked, with someone making more than 2000 unauthorised attempts to access Budget-related information.

He had referred the matter to police.

Last night Finance Minister Grant Robertson said in a statement that he had asked the National Party not to release any further material, "given that the Treasury said they have sufficient evidence that indicates the material is a result of a systematic hack and is now subject to a Police investigation".

Bridges said Robertson had clearly implied that the National Party had hacked Treasury, or had received hacked information.

"Grant Robertson has made scurrilous false allegations. He has smeared the National Party," Bridges told media this morning.

"There has been no hacking under any definition of that word. There has been entirely appropriate behaviour from the National Party. There has been nothing illegal or even approaching that from the National Party at any time."

Bridges said Robertson was smearing National and went so far as to say Robertson was "lying".

"What annoys me here, frankly, is that it should be Grant Robertson here right now explaining and front up, because he is misleading New Zealanders. In fact, I would go as far to say he is lying."

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Though he would not say how National had obtained the information, Bridges repeatedly said that National had acted legally and appropriately, and National had not done anything resembling hacking, nor had it received potentially stolen or hacked information.

"We are seeing a bungling, incompetent Government," Bridges said.

"The reality is they are incredibly embarrassed, they are not in control of what they are doing, so they are lashing out and are having a witch-hunt on the National Party."

He said the Government was trying to "gag" the Opposition.

"And that is an undemocratic outrage."

Bridges added that Treasury had also made incorrect statements and should also front up with Robertson.

"They are in a frenzy ... Typical of the Labour Party when that happens, they then decide to lash out. They are going for it. They will have got Treasury and others in, and they will be looking for scapegoats, for people to blame."

Bridges added that he did not intend to release any further Budget information today, which is what Robertson asked of him last night.

He said he was the minister in charge of cyber security for former Prime Minister Bill English, and Treasury would not have called in the police if it was only about hacking, which was attempted all the time.