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| Symbolic image of hacking | Photo: Reuters |
The incident occurred in early December. The matter came to light after the Finance Ministry sent a letter to lawmakers informing them of the incident.
The US Treasury Department has described the hacking as a "major incident" and said it is working with the FBI and other agencies to investigate its impact.
A spokesperson for the Chinese embassy in Washington DC told BBC News that the allegations were made as part of a smear campaign and was "baseless".
Meanwhile, the US Treasury Department said in a letter to lawmakers that the China-based hacker group was able to hack the department's systems using external service providers. Using these services, employees can access the department's systems from outside the office and work.
US officials said the outside service, called BeyondTrust, has been shut down since the hack, adding that there was no evidence that the hackers had accessed the department's systems.
Cybersecurity and infrastructure security agencies and outside forensic investigators are working with the FBI to examine the full impact of the incident.
Based on the evidence available so far, US officials say it appears that a Chinese state-sponsored hacker group (APT) carried out the incident.
A ministry spokesman told the BBC that BeyondTrust had alerted the Finance Ministry about the hacking threat on December 8. According to the company, suspicious activity was first noticed on December 2. However, it was not until three days later that the company realized it had been hacked.
The spokesperson added that the hacker group could access the workspaces of many Finance Ministry employees and certain non-confidential documents they were keeping. However, the ministry did not say which documents were accessed by the hackers and how long the hacking lasted.