The Chinese People's Liberation Army (PLA) Rocket Force has conducted a nuclear attack survival exercise where troops in an underground missile facility had to endure extreme conditions and make sure they could still launch nuclear counterattacks.

During the undated exercise, a Rocket Force brigade mobilized into the launch bunker at an undisclosed location and completely sealed themselves off from the outside world, as the troops readied for combat, China Central Television (CCTV) reported on Wednesday.

The bunker was then struck by a mock hostile nuclear attack as the troops inside, fully dressed in protection suits, carried out contingency plans and operated missiles for upcoming counterattacks, according to the report.

They also simulated a situation where missile fuel leaked after a hostile strike and a troubleshooting team was immediately deployed to repair.

Tactics including a fast missile condition check, rapid logistics, bunker defense and hasty launch were also practiced, CCTV reported.

While China is one of a few countries in the world that operate nuclear weapons, it has promised no first use, a military expert who asked not to be named told the Global Times on Thursday.

It was crucial the force survive an initial hostile strike to launch a counterattack, the expert noted. Such exercises ensure that capability and contribute to China's nuclear deterrence, the expert said.

China has a series of defense facilities located deep under mountains dubbed the "Underground Steel Great Wall," which "guarantee the security of the country's strategic arsenal" against potential attacks, including those from hypersonic weapons, Qian Qihu, a key architect of the fortifications who won China's highest science and technology award of 2018, told the Global Times in a previous interview.

At the National Day military parade on October 1 last year, China displayed the DF-5B silo-based nuclear-armed intercontinental ballistic missile.

The parade also showcased the DF-31AG and DF-41 road-mobile ICBM, DF-26 nuclear/conventional intermediate-range ballistic missiles (IRBM) and JL-2 submarine-launched ballistic missile (SLBM).

No nuke is expected to be ever used again, but China needs to protect itself by retaining its nuclear deterrent, developing and practicing with the weapons, analysts said.