The cost of extending Shanghai's magnetic levitation - or maglev - railway may more than double, says a report in the China Daily newspaper.
Shanghai's maglev train started commercial service in 2003
The state-run publication said the price could increase to 500m yuan ($69m; £35m) per kilometre of the 31.8km extension, up from 200m yuan.
It puts the increase down to a revised route to avoid densely populated areas.
Maglev trains use electric-powered magnets to float above their tracks, allowing for super-fast speeds.
The newspaper report said the cost increase had also been caused by plans to increase the buffer zone around the track, to take into account residents' concerns about exposure to electromagnetic radiation and noise.
Shanghai currently has the world's only commercial maglev service, where the floating train has whisked travellers between the city's main airport and the financial district since 2003.
The planned extension will connect with the city's second airport.
The Chinese government and a German consortium including Siemens, which helped develop maglev technology, have also discussed the possibility of extending the line by 160km to the city of Hangzhou.
Last year, Germany said it had come up with the funds to launch its own maglev rail service.
The state of Bavaria is to build the high-speed railway line from Munich city centre to its airport.
Japan is also now actively exploring the introduction of maglev services.
The world's first commercially operating maglev railway was at Birmingham International Airport in the UK.
From 1984 to 1995, it shuttled passengers 600m from the main terminal to the nearby railway station.
But after 11 years in operation, it was hit by reliability problems and replaced by a conventional system.
Although maglev allows for speeds substantially higher than traditional railway lines, critics point to its much higher costs of installation.
Munich is following in Shanghai's footsteps
HOW MAGLEV TRAINS WORK
Opposite poles on magnets keep train above track
Train is propelled by electro-magnetic system in the sides of the "guideway" instead of onboard engine
Top speed (with passengers) - 450km/h (280mph)
Developed by Transrapid Int in Germany
Operating commercially in Shanghai
Test facility in Emsland, northern Germany, is longest of its kind at 31.5km (19.5 miles)
Source: Transrapid International