Firefighters are raising the alarm, that Christchurch's only high-reach fire truck ladder is out of service

The Professional Firefighters Union says Fire and Emergency's failing to provide an adequate replacement, while the 32 metre ladder truck is off duty for maintenance.

The union says the garden city has only a short-crewed ute that cannot perform critical tasks, including rescues from multi-storey buildings, or fighting fires from above.

They claim the maintenance was planned, meaning Fire and Emergency had every opportunity to prepare and provide cover, but failed, leaving the city vulnerable.