Add some Xamarin Forms UI in a WPF application

We have a large WPF application that we are planning to move to Xamarin Form to be able to cross-platform.
But this will need time....
In the meantime, we would like to develop all the new UIs in Xamarin forms and navigate to these pages from our existing WPF pages.
I defined a Xamarin+WFP page as "public partial class WPFXamarinPage : FormsApplicationPage" and tried to navigate to the Xamarin forms with Frame.NavigationService.Navigate(new WPFXamarinPage()); but that does not work.
That does not work.
how should I proceed?