In 2012, China had thousands of miles of deep underground tunnels connecting bases.

"China's Underground Great Wall: Subterranean Ballistic Missiles"

https://www.belfercenter.org/publication/chinas-underground-great-wall-subterranean-ballistic-missiles

https://www.npr.org/2011/12/22/144141325/team-ignites-debate-over-chinas-nuclear-tunnels

https://igcc.ucsd.edu/_files/PPNT/NuclearBriefing2presentation1.pdf

https://www.rand.org/content/dam/rand/pubs/research_reports/RR1600/RR1628/RAND_RR1628.pdf

"In December 2009, a report by Chinese state-run channel CCTV claimed that China had more than 3,000 miles of tunnels including deep underground facilities that could withstand several nuclear attacks. It even opened their underground facilities to journalists in order to publicize the achievements of the country in regards to reinforce the survival of its nuclear arsenal and, therefore, maintain the credibility of its deterrence."

https://www.globalsecurity.org/wmd/world/china/underground-great-wall.htm

https://carnegieendowment.org/2011/10/26/underground-great-wall-alternative-explanation-pub-45816

https://www.washingtonpost.com/world/national-security/georgetown-students-shed-light-on-chinas-tunnel-system-for-nuclear-weapons/2011/11/16/gIQA6AmKAO_story.html

https://www.dailymail.co.uk/news/article-2258793/U-S-military-need-look-ways-neutralize-Chinas-underground-storage-facilities-contain-3-000-nuclear-weapons.html

https://defence.pk/pdf/threads/pla-underground-great-wall-analysis.509270/

https://en.wikipedia.org/wiki/Underground_Great_Wall_of_China