A leading US lawmaker who fears budget cuts could delay modernizing the US nuclear arsenal voiced concern Friday about an extensive tunnel complex designed to house Chinese nuclear missiles.

"This network of tunnels could be in excess of 5,000 kilometers (3,110 miles), and is used to transport nuclear weapons and forces," said Michael Turner, who chairs a House Armed Services Committee panel focusing on strategic weapons and other security programs.

"As we strive to make our nuclear forces more transparent, China is building this underground tunnel system to make its nuclear forces even more opaque," he added, citing an unclassified Department of Defense report.

Experts also expressed their concern about the network, whose existence was revealed by official Chinese media in late 2009.

The tunnels would allow China to launch a nuclear counter-attack if it was hit by a nuclear strike. "It's almost mind-boggling," said Mark Schneider, senior analyst at the National Institute for Public Policy.

"It has enormous implications in terms of their view toward nuclear warfare, survivability of their systems and their leadership in the event of war.

"It is virtually impossible to target anything like that, irrespective of how many nuclear weapons you have," he added.

Richard Fisher of the International Assessment and Strategy Center said the tunnel complex could allow the Chinese army to conceal its weapons.

"Do we really know how many missiles the Chinese have today?" he asked.

Turner expressed concern that planned cuts to the Pentagon could block efforts to modernize the US arsenal.

"We need to understand the potential long-term consequences of watching as Russia and China modernize their nuclear arsenal while we sit back and simply maintain our existing and aging nuclear forces," he warned.