NASAs version of this is called StarTram, it's feasible but there are some major technical hurdles.

In the prototype stage, the launch velocity at the end of the gun would not be anywhere near the 10 km/s you would need to achieve orbit. But you could reach a sizable fraction, say 3 km/s. Becuase the velocity gained during rocket flight is not linear with mass, having that 3 km/s inital boost would reduce your overall rocket mass by like 80%. The rocket would clear the atmosphere and then fire its motor to gain a stable orbit.

We can achieve 3 km/s with current technology, it would require like a 100 km long maglev in a very low pressure tube, likely built on the side of a mountain. It could probably reduce space flight costs by a factor of 10 if completed.

Building the proposed goal of a human rated version capable of reaching near 10 km/s at the end point would be much more difficult. The tube would have to span over 1,000 km and I don't believe we have the technology yet to maintain the vacuum or supply enough power quickly enough to power it.

China is likely proposing to build a testbed system to start researching the concept. Probably on a larger scale than NASA has but nowhere near a complete system.