The warning was contained in a Statement of Principles on Access to Evidence and Encryption and was part of a lengthy declaration issued after a meeting of ministers from the five countries in the Gold Coast on 28 and 29 August.
"The governments of the Five Eyes encourage information and communications technology service providers to voluntarily establish lawful access solutions to their products and services that they create or operate in our countries," the statement said.
"Governments should not favour a particular technology; instead, providers may create customised solutions, tailored to their individual system architectures that are capable of meeting lawful access requirements. Such solutions can be a constructive approach to current challenges.
It left open the door for enforcement agencies to use specific cracks to gain access to encrypted communications on specific devices.
Representatives of technology companies were invited to last week's meeting but did not attend.
In the main communique issued after the meeting, the five governments said: "Encryption is vital to the digital economy, a secure cyberspace and the protection of personal, commercial and government information.
"The five countries have no interest or intention to weaken encryption mechanisms. We recognise, however, that encryption, including end-to-end encryption, is also used in the conduct of terrorist and criminal activities.
"The inability of intelligence and law enforcement agencies to lawfully access encrypted data and communications poses challenges to law enforcement agencies' efforts to protect our communities.
"Therefore, we agreed to the urgent need for law enforcement to gain targeted access to data, subject to strict safeguards, legal limitations, and respective domestic consultations."