declare module vs declare namespace typescript

I am little confused about the difference between declare module and declare namespace in typescript internal modules.

Another point which i am not clear: is it a good idea to have complex namespaces to typescript internal modules. e.g.

    declare module com.xyz.company.test.mynamespace {
     interface Iabc {// stuff }
     interface Ixys{ //stuff }

    // or

    export interface Ipqr { // stuff }
 }

from declare module vs declare namespace typescript