The London Ambulance Service says it expects its 999-call computer system to be back up and running "in the next hour or two."
A spokesman said that the technical issue had been identified and that they were now bringing the system live again.
More top news
Singer knocks Oasis from their 18-year hold on the top spot as her third album sells more than 800,000 copies in its first week of release
Teenage twin brothers were found guilty today of murdering a 'quiet, humble' father who dared to intervene in a robbery in north London.
The women were reportedly both students at City and Islington College campus in Holloway Road.