A "major incident" was declared by North West Ambulance Service (NWAS) due to a large number of calls on Monday evening.
In a statement posted to Twitter and Facebook, NWAS said that if callers had a non life-threatening concern, they may be asked to seek treatment elsewhere or make their own way to hospital.
A spokesperson later said that the incident had been stood down.
They had earlier said there was "currently nothing to indicate this increase in calls is in relation to COVID-19", and that "Mondays are often a very busy day".
On Facebook, the service added that the spike in 999 calls was particularly in the Greater Manchester area.
People were also being urged to call 111 for medical advice.
It is not clear what caused the influx of calls.
The spokesperson for NWAS had said: "We are putting in place additional support throughout the North West and will be closely monitoring the situation throughout the evening."
They went on: "There are patients who are facing a delay and we are very sorry that we are unable to respond as quickly as we would like."
The NWAS Union, which represents members of the service, also tweeted: "Please help our crews by only calling if you really need us. They are being run ragged at the moment and they will get to you as soon as they can.
"Please consider using 111 First. Thank you."