Is there a Express-style nested router for Koa.js?

Is there exist a library that provides Express-style nesting routers? Something like this:

var koa = require('koa');
var app = koa();
var Router = require('???');

var restApiRouter = new Router();
restApiRouter.get('/', function*() {
  // respond to /api/
});
restApiRouter.get('/messages', function*() {
  // respond to /api/messages
});

var appRouter = new Router();
appRouter.get('/', function*() {
  // respond to /
});
// redirects all /api/* requests to restApiRouter
appRouter.use('/api', restApiRouter);

app.use(appRouter);

If there isn't, what is the best practice to incapsulate common path routes in other files?