There are times where a situation is so urgent that it requires an immediate call to arms. Sending out a meeting invite, waiting for the participant to read, accept and join is just not acceptable.
In times like this, you just need to set up a meeting a drag people in and get on with it. There is a feature in Teams called “Meet Now” for this purpose.
To launch a Meet Now, go to the Calendar app on the Teams client and click the button called “Meet Now‘

A popup will open where you can optionally give the meeting subject more context and then two call to action buttons. It is recommended to first copy the meeting share link to your clipboard as you can send this via Chat directly to the people you need. Then click start meeting to launch the Teams meeting.

When the meeting launches it will open the participant blade and you can search by name for the people you need to drag into the meeting. When you do this, the meeting will call each participant as you add them and on their acceptance, automatically join them into this meeting.

It is also possible to create a Meet Now directly from a Channel in a team.