WASHINGTON (AFP) - A leading US lawmaker who fears budget cuts could delay modernising the US nuclear arsenal voiced concern on Friday about an extensive tunnel complex designed to house Chinese nuclear missiles.

'This network of tunnels could be in excess of 5,000km, and is used to transport nuclear weapons and forces,' said Mr Michael Turner, who chairs a House Armed Services Committee panel focusing on strategic weapons and other security programmes.

'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 Defence report.

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