Up to 300 people could lose their jobs.
Newshub said it had not asked Prime Minister Christopher Luxon for financial help, and the government appears to have no intention of stepping in.
Journalists, commentators and some politicians said the closure was bad news for democracy and a forewarning of worse to come.
MPs shared their sympathies - and their concerns over the wider implications of one the country's major TV news services shutting down.
Broadcasting Minister Melissa Lee said it was something outlets around the globe were experiencing.
"I think journalists actually losing jobs - as a former journalist - I actually feel for them, I just think it's a sad day.
"Having said that, plurality is not an issue, because the way that people consume media has actually changed. We're no longer sitting in front of a television box watching the news at 6 o'clock.
Lee was given a heads-up by network chief Glen Kyne on Tuesday night - before he broke it to the newsroom late on Wednesday morning.
She said Warner Bros Discovery did not ask the government for financial assistance - and she was clear it cannot intervene.
"He said there was nothing that could have actually helped, it was actually a failure in terms of the way they're advertising for their news, it was actually a massive drop and nothing could have actually helped."
And Labour's broadcasting spokesperson, the former minister, told Morning Report his party wouldn't have bailed Newshub out either.
"I think it's probably a bit much, you and I both know, anybody would know, you've got a $20m company behind Newshub," Willie Jackson told Morning Report.
He said they would have brought the company in and tried to help them find a way through.
Jackson questioned Lee's commitment to finding a solution.
Labour introduced a Fair Digital News Bargaining Bill - which would require social media platforms to pay news outlets to use their content.
But Jackson said the current government was not interested in the bill, which was currently before a Select Committee.
He said Newshub briefed him about financial difficulties last year - but the closure was a surprise.
"They did say things were not going too well, they didn't ask for any assistance in terms of funding but they were pretty clear that things were not too good."
Coalition's thoughts: disaster
Deputy Prime Minister Winston Peters framed the situation as a disaster for the staff and New Zealand.
"A critical part of any democracy and free society is the fourth estate, an independent fourth estate, and I'm concerned about where we're going now," he said.
"Frankly for those 300 or so staff and their spouses and their families, this is an absolute disaster. But it's also a disaster for this country's democracy."
Associate finance minister David Seymour said while the government would not buy out Newshub, he had requested advice on whether government-owned TVNZ should start returning a dividend, to help level the playing field.
"I think there's a question mark around whether the government's ownership of one TV channel and the poor returns it's demanded as a shareholder has actually contributed to an uncompetitive market."
Sad day
Deputy Labour leader Carmel Sepuloni told First Up the probable Newshub closure was sad and disappointing for those losing their jobs, and democracy.
"In this day and age when we're bombarded with information, some of which is not true, it's really important that we've got trusted sources of information and now we're not going to have that through Newshub."
She said while it was not always comfortable when journalists asked questions, they were "doing their job".
"Respect for the work they do and it's fundamental, like I said, for our democracy."
Labour leader Chris Hipkins said it was a sad day for democracy.
"I want to extend my thoughts to everybody who's been affected by that announcement, I know that it will be a really uncertain time for them."
