Heavy rain in the headwaters of Canterbury’s major alpine rivers has prompted a flood warning, with flows expected to rise overnight and into Tuesday.

Environment Canterbury said rain had been falling across the, Hurunui, Waimakariri, Rakaia, Rangitata and Waitaki headwaters since Monday evening and was expected to continue through the night before easing in the morning.

The heavy rainfall is also expected to spill into the headwaters of smaller foothill rivers.

Flows are forecast to increase in the upper reaches overnight, with lower sections expected to rise from Tuesday afternoon.

Authorities said they were closely monitoring forecasts, rainfall totals, river levels, and flood protection infrastructure.

Residents and farmers are being advised to stay alert for changing river conditions, especially if working or spending time near riverbeds.

Farmers with stock near flood-prone areas are urged to move animals to higher ground as a precaution.

For detailed forecast information and ongoing updates, people are encouraged to visit the MetService website.