North West Ambulance Service (NWAS) declared a major incident due to the high level of 999 calls on Monday.
It said it was "exceptionally busy" and warned the public to only call if "their condition is life-threatening or potentially life threatening".
NWAS said it was unsure of the reason for the "sudden surge" - particularly in Greater Manchester - but said Covid-19 accounted for about 15% of calls.
Shortly after 21:00 GMT calls had reduced towards normal levels.
NWAS said it received more than 2,200 calls between midday and 20:00 GMT, a 36% increase on the same period last Monday.
⚠️We've declared a major incident due to the high level of calls. For enquiries relating to this incident, please follow us here/our Facebook page.— North West Ambulance Service (@NWAmbulance) November 2, 2020
⚠️If your call is not life-threatening, you may be asked to seek an alternative source of care or make your way to hospital. pic.twitter.com/bEHYcKGg4e
A statement on Facebook said: "You can help us reach the patients that urgently need our help by not calling 999 unless the condition is life-threatening or potentially life-threatening, not calling us to find out where your ambulance is or calling to cancel any ambulance that you no longer require or feel is necessary.
"We are trying our best to reach patients as soon as we possibly can and apologise for any delays in our response. Please bear with us."
The NWAS branch of Unison 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."
Staff had agreed to cancel breaks for two hours between 17:00 GMT and 19:00, the union said.