A flood alert has been issued for parts of Rochdale, Oldham, Bolton and Bury.
The Environment Agency has warned water levels on River Irwell are rising following heavy downpours.
And that could lead to flooding on low-lying roads and land.
Residents are being warned flooding is possible around the rivers Beal, Roch and Croal and at Limy Water.
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Other areas that could be affected include Farnworth, Whitefield, Little Lever, Radcliffe, Heywood and Whitworth.
Residents are being warned not to use footpaths or bridges nears rivers and to avoid walking or driving through flood water.
The flood alert, which covers the upper River Irwell catchment area, says: "River levels are rising on the River Irwell due to heavy rainfall.
"Flooding is possible at low lying land and roads around the Rivers Beal, Roch and Croal, Limy Water and their tributaries today, Monday, November 1.
"Further heavy rainfall is forecast today.
"Avoid using low lying footpaths and any bridges near local watercourses and do not attempt to walk or drive through flood water. Our incident response staff are closely monitoring the situation.
"Upper Irwell catchment includes the Rivers Beal, Roch and Croal, Limey Water and their tributaries. Other locations which may be affected are around Farnworth, Whitefield, Little Lever, Radcliffe, Bury, Heywood, Whitworth and Bacup."
It comes as torrential rain hit much of Greater Manchester on Monday morning.
Further downpours are forecast throughout the rest of the day.
Train services have also been cancelled between Bolton and Preston due to flooding on the railway.
