The mid-year economic and fiscal outlook (MYEFO) said an extra $750 million would be spent in 2019-20 "to accelerate critical infrastructure projects across Australia to drive jobs, strengthen the economy and get people home sooner and safer".

The Coalition had been working with states and territories to identify key projects to bring forward, in an attempt to jump-start the sluggish economy.

But the state-by-state breakdown within the budget papers showed only $702 million had been brought forward under the Infrastructure Investment Program since the last budget.

Asked to explain, the Infrastructure Department said the missing money was going to two different budget measures - "Norfolk Island - Essential Services" and "Supporting Infrastructure Investment and Services".

The first would provided $6.8 million over three years from 2019-20 to improve Norfolk Island's water, emergency management, health, aged care, prosecution and communication services. Norfolk Island would also get $2.6 million over two years from to develop a detailed business case for a new multipurpose health centre and $3.3 million over three years to improve cruise ship transfers.

The second measure provided $34.5 million over four years from 2019-20 (and $7.4 million per year ongoing) to "support infrastructure investment and services, promote significant national and local infrastructure programs and provide additional resourcing for the implementation of priority projects".

It was first announced in last year's mid-year budget update, where it said the money would also be used for a "public awareness campaign" to advertise the transport projects the government was delivering.

But while these budget measures added up to $47.2 million, the money was spread over four years. Only $23.4 million was actually earmarked for this financial year, meaning it could not be the apparent shortfall.

When The Canberra Times pointed this out, the department then came back with a list of additional projects which did indeed bring the total to exactly $50 million.

It included an extra $12 million to help the Civil Aviation Safety Authority regulate commercial drone technologies.

It also included $4 million this financial year to support economic diversification on Christmas Island (part of a $12 million over the next three years). Projects include improvements to tourism infrastructure, a business case for a science research centre, and the establishment of a business innovator and entrepreneur network.

There's also $6.4 million in 2019-20 to help Tasmania increase its freight supplies for high density goods being shipped in and out of the state (in total $21.7 million over the forward estimates).

Labor's infrastructure spokeswoman Catherine King said it showed the Coalition's infrastructure program was "all smoke and mirrors".

"They don't have a real plan for infrastructure and now their budget doesn't even add up," Ms King said.

But a spokesman for Infrastructure Minister Michael McCormack said: "all infrastructure portfolio measures are aimed at creating jobs, supporting local businesses and securing sustainable futures for communities".

MYEFO also showed there was no accelerated funding for the ACT other than the $30 million for the Monaro Highway in 2020-21 over the forward estimates. The ACT is the only jurisdiction not to receive money in this financial year for projects.

Ms King said MYEFO confirmed the promise to bring forward infrastructure was a sham, with "with barely any additional funding this financial year and nothing for the ACT".

"Not a cent will flow to the ACT until mid-next year at the earliest," Ms King said.

"$750 million represents just 18 percent of the headline figure from the prime minister's infrastructure announcements last month, and is only an 11 percent increase in this year's infrastructure budget. That's if this government can even deliver that."