Boris Johnson has given the green light to 20 new building and infrastructure projects in the NHS in England.
The £850m package will pay for new wards, intensive care units and diagnostic centres as well as refurbishing some existing facilities over the next five years.
"It's part of a programme that the NHS asked for and I want to stress this is new money," the prime minister said.
But doubts have been raised over whether the money really is new.
Mr Johnson also said there would be an extra £1bn this year to improve and maintain existing buildings.
The government had already committed to £6.7bn being spent on building and infrastructure, including IT, during 2019-20.
But despite repeated requests, Number 10 has been unable to confirm whether that total figure will rise.
Mr Johnson said the new money - less than 1% of the annual NHS budget - would mean "more beds, new wards, and extra life-saving equipment".
"It's time to face up to this challenge and make sure the NHS receives the funds it needs to continue being the best healthcare service in the world," he said.
Mr Johnson previously said he was "determined to deliver" on the promises of the 2016 EU referendum, after criticism of the Vote Leave campaign's claim that £350m a week was being sent to the EU and could be spent on the NHS instead.
Health Secretary Matt Hancock said the NHS was "priority number one" for the new prime minister.
He said money for hospital upgrades was possible because the economy was growing and the funds would be available this year.
Responding to the funding announcement, the Health Foundation said "years of under-investment in the NHS's infrastructure means this extra money risks being little more than a drop in the ocean".
Ben Gershlick, from the charity, added that NHS facilities in England were "in major disrepair", with a £6bn maintenance backlog.
Labour's shadow health secretary, Jonathan Ashworth, said there was "huge scepticism" about whether the funding was new.
Meanwhile, Labour leader Jeremy Corbyn said the announcement today on funding for the NHS "goes nowhere near paying for all the cuts over the past nine years".
Mr Corbyn said "many hospitals had been left off" and "we need something a bit more comprehensive".
But the head of NHS England, Simon Stevens, said the money was a "significant start" to "much needed capital investment".
The government said other parts of the UK would benefit too.
Health is devolved, so Wales, Scotland and Northern Ireland make decisions about spending on the NHS.
But under funding rules there would be money made available to them, ministers said.
Later this week, the government is also expected to announce changes to the NHS pension scheme after senior doctors said new rules meant they could not afford to work extra shifts to tackle waiting lists.
One hospital said the rule change, which means "punitive" taxes for doctors who take additional shifts and exceed the limit for pensions contributions, was the equivalent of losing 60 consultants.
Mr Johnson has previously pledged to resolve the problem.
