A new phone number has been introduced by the Metropolitan Police for callers to use in non-emergency situations.
Police hope the number - 0300 1231212 - will make it easier for Londoners to contact them and reduce the number of inappropriate 999 calls.
Commander Simon Bray said callers will be transferred to the appropriate team.
He said: "In an average month we get about 200,000 emergency calls and about a quarter of those are calls which do not require an emergency response."
A Met spokesman said people should always dial 999 in a genuine emergency - when a crime is taking place, when a crime suspect is nearby or someone is injured, being threatened or in danger.
In all other situations the new 0300 1231212 number should be used.
Local police stations and Safer Neighbourhood Teams can still be contacted via their direct numbers, he added.
In 2006 Northumbria Police introduced a non-emergency 101 number.
It experienced a subsequent rise in the number of 999 calls it received. Police said this may have been due to the continuing popularity of mobile phones.