<p>With the advanced development of quantum science, constructing a large-scale quantum network has become a prominent area in the future of quantum information technology. Future quantum networks promise to enable a wide range of groundbreaking applications and to unlock fundamentally new technologies in information security and large-scale computation. The future quantum internet is required to connect quantum information processors to achieve unparalleled capabilities in secret communication and enable quantum communication between any two points on Earth. However, existing quantum networks are primarily designed to facilitate communication between end users within their own networks. Bridging different independent networks to form a fully connected quantum internet has become a pressing challenge for future quantum communication systems. Here we demonstrate the quantum fusion of two independent networks based on multi-user entanglement swapping, to merge two 10-user networks into a larger network with 18 users in a quantum correlation layer. By performing Bell state measurements between two non-neighbouring nodes, users from different networks can establish entanglement, allowing all 18 users to ultimately communicate with each other using the swapped states. Our approach opens up promising opportunities for establishing quantum entanglement between remote nodes across different networks, facilitating versatile quantum information interconnects and enabling the construction of large-scale intercity quantum communication networks.</p>