Staff with one of the country's biggest ambulance services had to log emergency calls manually overnight after technical issues in the control room, delaying response times.
It is understood London Ambulance Service's computer system crashed, forcing staff to record details of calls by pen and paper for nearly five hours on one of the busiest nights of the year.
A spokeswoman said staff are trained to deal with such situations and they were able to prioritise responses to those in greatest need.
Deputy director of operations Peter McKenna said: "Due to technical difficulties, our control room was logging emergency calls by pen and paper from 12.30am to 5.15am.
"Our control room staff are trained to operate in this way and continue to prioritise our response to patients with life-threatening conditions, using the same triage system as usual.
"We also have additional clinicians on duty to offer control room staff clinical advice if it is needed."