He told the BBC an "enormous amount" of money was being spent on the high speed train line and it was important to make the right long-term decision. Pressure is growing on the PM to make an announcement as reports continue to circle that he is going to scrap the line's Birmingham to Manchester leg. But the PM refused to confirm whether it would go ahead.
Repeatedly asked on BBC Breakfast to confirm whether HS2 would continue all the way to Manchester, he said: "I know there's lots of speculation but all I can say is I'm not going to be forced into a premature decision because it's good for someone's TV programme.
"What I want to do is make the right decision for the country."
Mr Sunak denied the issue had been a distraction from his party's annual conference in Manchester and that the handling of any announcement had been poor, insisting "we're having a great conference".
There is frustration from both Tory supporters and opponents of HS2 that the issue has been allowed to overshadow the party conference, which could be the last before the next general election, due in 2024.
After weeks of speculation and leaks, there were reports on Monday an announcement on the future of HS2 was imminent - but Downing Street insisted no final decision had been taken.
There is now a growing expectation confirmation could finally come in the prime minister's conference speech on Wednesday.
If there is a decision to scale back the project this could be accompanied by a pledge to invest in other transport schemes in the north of England to combat accusations the government is abandoning its mission to level up the country.
In recent days, ministers have answered questions on HS2 by highlighting the importance of east-west links.
For example, Northern Powerhouse Rail (NPR) aims to improve connections between Leeds, Manchester and Liverpool.
However, the project has been designed to intersect with HS2, using a section of the high speed line, and if HS2 does not continue to Manchester this would increase the costs of NPR.
A number of senior Conservatives have urged the prime minister not to scrap the Manchester leg.
Former Chancellor George Osborne said HS2 was "a great opportunity to deliver for northern voters" and cancelling phase two to Manchester "would be a great tragedy".
He added that NPR was not a substitute for HS2 and that both projects "should go ahead together".
In a dramatic intervention on Monday, West Midlands Tory mayor Andy Street said axing the Manchester leg would amount to "cancelling the future" and risk damaging the UK's international reputation "as a place to invest".
Mr Street acknowledged the costs were "escalating" but said he had been working on a new funding model for the project with more private sector involvement.