Police have declared a major incident due to concerns about the impact of Storm Christoph.
An amber weather warning for rain has been issued as torrential downpours are set to hit the region.
It's in force until Thursday lunchtime, with forecasters warning of potential flooding.
A top police chief urged people to leave their home if they need to despite the stay at home message.
Residents are being urged to follow their local authority's advice about evacuations.
Assistant Chief Constable Nick Bailey, Chair of the GM Strategic Coordination Group for Storm Christoph, said: "In order to ensure that we're as prepared as possible for the heavy rainfall expected from Storm Christoph, we have declared a major incident.
"The safety of the public is our number one priority and we're continuing to work alongside partner agencies across the region.
"Whilst we appreciate that everyone has been told to stay home due to the coronavirus pandemic, we want to make it clear that should members of the public need to evacuate to protect themselves due to flooding then that is the priority and you should follow your local authority's advice regarding evacuation.
"Coronavirus remains a threat to everyone's health and people should not leave their homes unless it is absolutely essential, but where there is a risk of flooding, that is clearly essential and we're working with our partners to ensure that people can do this as safely as possible.
"For anyone that needs to evacuate, we'd ask that you remain very aware of Covid-19 and continue to follow the government guidance around Hands, Face, Space as much as possible and limit your contact with other people."
Anyone with concerns is asked to contact their local council.
Chief Con Bailey added: "We would continue to urge anyone with concerns about flooding in their area to contact their local authorities who will be able to sign-post you to the most appropriate information and support.
"Partner agencies are working hard on local plans to ensure that people living in potentially vulnerable areas are notified at the earliest opportunity.
"Heavy rainfall is expected from later today and that could cause flooding in several areas across Greater Manchester - we are preparing for this and are continuing to monitor the situation very closely. We will continue to provide updates as often as we can."
