It marks a significant development for the social media giant, which since 2012 has owned the popular Vine app, which can record videos lasting five or six seconds.
Of the new feature, Twitter said: "In just a few taps you can add a video to unfolding conversations, share your perspective of a live event, and show your everyday moments instantly, without ever having to leave the app. Viewing and playing videos is just as simple: videos are previewed with a thumbnail and you can play them with just one tap.
"Our unique mobile video camera and inline editing experience lets you capture and share videos up to 30 seconds in an instant. Twitter for iPhone users will be able to upload videos from the camera roll as well (a feature that will be available on our Android app soon)."
The first tweet using the mobile video camera is from Oscars host Neil Patrick Harris:
Separately, Twitter is launching a group direct messaging service, seen as a rival to Facebook’s WhatsApp.
New! Use Direct Messages to speak privately with a group of up to 20 people. Share Tweets, show emoji & be yourself. https://t.co/8giGhC6OO0— Twitter (@twitter) January 27, 2015
"We’re rolling these features out to all users in the coming weeks," Twitter said.