Cessna 310/T310C
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 50; Flight Crew Total 5300; Flight Crew Type 200
Situational Awareness; Time Pressure
Conflict NMAC
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Environment - Non Weather Related; Human Factors; Procedure
I was on a downwind for Runway XX at ZZZ and issued a visual approach clearance with restriction maintain 3;000 feet until turning base and told to contact Tower.  I turned base and started the descent.  Upon contacting Tower; I was instructed to immediately climb to avoid a traffic conflict below me.  I then noticed the traffic alert on my ADS-B screen 400 feet below me and climbed to avoid while on base.  Shortly after I was issued cleared to land on Runway XX for ZZZ.
C310 pilot reported a NMAC on base leg during the approach to land.