Starting next week, tourists driving into Milford Sound will be charged $10 an hour to park at the fiord in an effort to encourage them to hop on a coach or carpool instead.

Milford Sound Tourism (MST) is hoping that by putting a price on the limited number of car parks available at Milford Sound, more tourists will think twice about choosing to make the two-hour drive from Te Anau on their own.

MST general manager Tim Holland said the $10 per hour charge, which would begin October 1, would apply only to the area's three main car parks, which typically attracted tourists.

The 80 additional spaces at the gravel overflow carpark in Deepwater Basin Rd would remain free, with free courtesy coach transfer.

It's been well documented that visitor numbers to Fiordland's jewel in the crown have been on a steep rise over the last five years. 

According to MST, a large proportion of this visitor growth has been self-driving tourists. Despite the visitor growth, the average number of people per vehicle has plateaued at 2.1 passengers.

For MST, which provides the tourism infrastructure for the busy area, this has meant a disproportionately increased demand for the 241 paved car parks at Milford.

"Because we're not able to make any more flat land in Milford, we're actually having real trouble fitting them in," Mr Holland said. 

"This is really all about the visitor experience and ensuring everybody has a wonderful time, and doesn't spend hours driving around, looking for a car park that doesn't exist."

This week, MST is installing a "pay by plate" system that utilises cameras to recognise licence plate numbers. Tourists could either pay before they took off on the cruise or once they returned. If they left without paying, MST would have a record of the licence plate number and follow up on the issue. 

"We have chosen the most advanced system that we can that's barrier-less. It's completely paperless. What we didn't want is car parking tickets, which tend to be plasticated paper, blowing around Fiordland National Park and creating a menace."

MST would also install signage leading into Milford Sound to alert drivers to the new fees, along with having six car park attendants on deck this season.

MST would not know how much of an impact, if any, the fees would have until the system was operative and the data began to come in. 

Mr Holland said three or four of the coach operators he spoke to indicated they had the extra capacity to be able to cope with any additional demand, however he had not yet spoken to all of them.

He said he'd like to have those conversations about any changes in capacity once MST had data in hand early in the season. 

"Over the last few seasons, we've gone from 565,000 [visitors] to 780,000. That capacity didn't just magically appear in Milford. These people are agile business people and they understand the market and we have managed to get that amount of people into Milford. A lot of that has been in increases in coaches. That doesn't just happen by magic. I have every faith that the market will address any capacity changes."

The idea of charging for parking isn't new. Mr Holland said it had been mentioned in the Fiordland National Park Management Plan when it was released in 2007.

MST requested the concession from the Department of Conservation a couple of years ago and the decision to go forward with the concept for this summer season was made earlier this year.