China is losing more than $10 billion a year from its expressways, state media reported Wednesday, despite levying hefty tolls on the world's largest highway network.

China spent 431 billion yuan ($69 billion) on building, maintaining and operating highways in 2013, but only took in 365 billion yuan from tolls, the China Daily reported, citing the Ministry of Transport.

For years the building of roads, high-speed rail lines and other infrastructure projects helped China hit double-digit gross domestic product (GDP) growth.

But with the economy slowing and authorities working to fight graft, the government is increasing scrutiny on spending.

Laying one kilometre of highway cost about 91 million yuan in 2013, an 80 percent increase from 2011, according to the Ministry of Transport's annual report.

Under current regulations, local transport bureaux can collect tolls for 15 years to recoup the cost of building highways. But many have also applied for extensions for what they say are maintenance costs, the China Daily reported.

Experts said the move was really a loophole designed to fill local coffers rather than improve roads, and construction costs are often inflated in order to ensure continued toll collection, the newspaper said.

China has the longest highway network in the world with 156,500 kilometres (97,000 miles) of expressways, including more than 100,000 kilometres of toll roads.

It began collecting highway tolls in 1984 and nearly all roads built since hen have been funded by those fees, according to the Ministry of Transport report.

Many drivers bemoan the unubiquitous tolls fees, which can make driving between two cities or taking road trips prohibitively expensive.