Google is changing the way emails are composed in Gmail, making it possible to write a missive while referring to older messages.

Before the changes were introduced for some users on Tuesday, anyone writing an email who wanted to check something in a previously sent or received message, would have to save a draft, then go check that older email, then return to the draft.

In the new mechanism, emails being composed pop up in separate windows, similar to chat windows. This makes it possible to navigate around the rest of the Gmail app without losing sight of the new message.

"Saving a draft, opening the old email, and then reopening your draft wastes valuable minutes," Google product manager Phil Sharp wrote in a blog post, adding that the new, chat-like compose format also makes it easier for users formulating multiple drafts at once.

The new mechanism also makes it possible to quickly add inline images to emails, and adds other minor features such as profile pictures in contact auto-suggest.

Right now, the features are available to limited users as a preview. According to Sharp, other features will be added over the coming months, after which Google will "enable it for everyone".