Joe Biden teases possible 2020 run: Save your energy, 'I may need it in a few weeks'

"I appreciate the energy you showed when I got up here. Save it a little longer, I may need it in a few weeks," Biden said to applause at the International Association of Fire Fighters' annual legislative conference. "Be careful what you wish for."

Biden's speech to the firefighters comes as the former vice president is in the final stages of deciding whether to run for president in 2020. His future remains one of the biggest unknown questions of the 2020 race.

Friends and allies of Biden have expressed confidence he will launch a presidential campaign, but a formal announcement of his decision is unlikely to come before April.

This is a breaking news story and will be updated.