Locals investigated repair work supposedly being carried out on a high-rise building and allegedly discovered an illegal construction site that had dug a network of tunnels under the basement.

Panicked locals called the police who seized the construction tools and ordered engineers to inspect the property damage in Beijing, China, on May 4.

Even after the discovery, it appears that the builders attempted to continue with the project and returned several times in the following days before police finally caught many off, and ordered city council engineers to confirm if the building was still safe to live in.

It is believed that the owner of the building was planning to illegally extend the amount of space available by adding a further basement area, and had dug a 30-metre-long (98ft) tunnel under a retaining wall as they removed soil for the new construction.

Locals said that they had used the May Day holiday when many officials were not working to push ahead with the project and were angry that it took three days before police finally resolved the situation on May 7.

Plans are now underway to fill in the tunnel with concrete and the cost will be passed on to the company which was behind the illegal building, cops said.

One resident said: 'We were literally stunned when we walked into what we thought was a small project repairing water pipes, and found tunnels that just went on for ages.

'We must have walked 30 metres without reaching the end.

'When we finally found the workers, they were still digging more tiles, asked for Austin who was in charge and they told us he was not there today. That'swhen we called the police again.'

It is unclear what purpose the network of tunnels was supposed to serve, but in the Chinese capital space even underground is at a premium, and it is believed they wanted to extend the amount of space they had available to increase their rental income.

At present, Fengtai District has organised functional departments and local streets to set up a joint working group to investigate the incident and seriously deal with the relevant responsible parties in accordance with laws and regulations.