Can we customize Master page and Page Layouts with SPFx?

I am working on SharePoint Framework and have one take to do in this. I want to know that can we add our custom master page and page layouts in SharePoint Online using the SharePoint Framework ?

If yes, then can you guys please provide me some details or links to understand this ?

I have a requirement to have my own custom master page and layouts deployed in SharePoint Online using my custom client web part.

No, as of now there is nothing in SPFx to customize master page or page layouts. Also, Master Page and Page Layouts are old technique, which is not applicable for Modern Pages.

But SPFx framework comes with extensions (in preview as of now), which can be used to enhance UX of application. The SPFx extensions allow you to customize in following three direction:

1. Application Customizers: Overall page customization can be done using this like header/footers.
2. Field Customizers: For custom rendering of fields.
3. Command Set: For adding custom commands to the top ribbons or popup menus.

https://dev.office.com/sharepoint/docs/spfx/extensions/overview-extensions