Calderdale Council is asking residents and businesses at risk to activate their flood plans - turning off gas, water and electricity, and moving important items to safety.
The flood siren in Walsden sounded earlier this morning to urge residents to take extra care.
The Environment Agency says river levels are rising as a result of persistent rainfall which is forecast to continue through much of today.
Levels of Hebble Brook at Halifax were forecast to continue to rise until about 8am this morning. The area of concern includes Dean Clough Industrial Park and Dean Clough Mill.
Flooding of Hebden Beck was expected from 4am. The area most at risk is properties and roads by Hebden Beck.
Levels at Brearley are forecast to peak at mid-morning today. Area of concern includes the Tenterfields Business Estate.
The Environment Agency and Calderdale's flood warnings are monitoring the situation closely and will be updating their websites and social media channels throughout the day.