The attack, part of a sophisticated level of cyber hacks called advanced persistent threats (APTs), poses a serious danger to Singapore and could undermine national security, K. Shanmugam disclosed in a speech late on Friday.

"I can say that it is serious and it is ongoing. And it has been identified to be UNC3886," said Shanmugam, who is also the home affairs minister.

Shanmugam did not disclose the group's sponsors, but UNC3886 has been pinpointed by Mandiant, a cybersecurity firm owned by Google, as a China-linked cyber espionage group involved in global attacks.

"Even as we speak, UNC3886 is attacking our critical infrastructure right now," he said, adding that Singapore's Cyber Security Agency (CSA) and relevant authorities were dealing with the problem.

APTs are highly sophisticated and well-resourced actors that typically steal sensitive information and disrupt essential services such as healthcare, telecom, water, transport and power, Shanmugam said.

"If it succeeds, it can conduct espionage and it can cause major disruption to Singapore and Singaporeans," Shanmugam warned.

A successful breach of Singapore's power system, for example, could disrupt electricity supply and have knock-on effects on essential services such as healthcare and transport.

"There are also economic implications. Our banks, airports and industries would not be able to operate. Our economy can be substantially affected," he said.

He said that between 2021 and 2024, suspected APTs against Singapore increased more than fourfold.

A cyber breach on a public healthcare cluster in 2018 accessed the medication records of about 160,000 patients, including then-prime minister Lee Hsien Loong.

The attack on Singapore's critical infrastructure "highlights the extraordinary challenges posed by APT actors," said Satnam Narang, senior staff research engineer at US-based cybersecurity firm Tenable.

"Combating such stealthy opponents is becoming increasingly demanding as the scale and complexity of IT infrastructure that organisations and nations must defend continues to grow," he said.