Date: 202104
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Second aircraft: Commercial Fixed Wing
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Time Pressure
Second reporter function: First Officer; Pilot Flying
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Critical; Ground Incursion Runway
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Rejected Takeoff; Flight Crew Returned To Gate; Flight Crew Took Evasive Action; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was pilot monitoring for this leg ZZZ to ZZZ1; we taxied out to Runway XX we were given position and hold initially; once we were in position and lined up; I transferred control to the First Officer. We were then given takeoff clearance; I read back the clearance '[Flight ABCB] Cleared for takeoff' the FO advanced the thrust levers; and 'said Runway XX set thrust' I called thrust set heading Checks. Soon after that while I was waiting to make the 80 knots call the FO said 'I don't think Aircraft Y is going to Stop' I immediately looked to see what he was talking about. And I see Aircraft Y; approaching the runway at [taxiway] it had not yet to appeared cross the hold short line; it took a split second to see it was not going to stop; the nose was just to the runway edge; I called abort I have the aircraft. Applying maximum breaking and full thrust reverser; we stopped 200-300 feet short of the [aircraft] as its nose was reaching the edge of the runway; as we reached a full stop the tower asked us if we could accept an intersection takeoff; we declined and exited the runway ran the aborted takeoff checklist and called Operations; they directed us to return to the gate.I am not sure why Aircraft Y flight crossed the runway we never heard them on the radio.


Second narrative: We were cleared for takeoff on Runway XX and proceeded our takeoff roll. I noticed Aircraft Y approaching from my right at a rate of speed that concerned me. I quickly brought it to the attention of the Pilot monitoring and Captain. I wanted him helping to make decisions in this situation. We immediately came to the same conclusion as I called to abort the takeoff. We immediately went to idle then full reverse with max braking and were able to stop before impact. Aircraft Y wasn't on our frequency and proceeded across the runway. I notified Tower of the abort and they asked if we could continue from there and we declined. We decided it was safe to exit the runway. We cleared the runway and preformed the appropriate checklist. Then returned to the gate as directed by Operations.ATC apparently cleared us on separate frequencies.


Synopsis: CRJ-700 flight crew reported a Critical Ground conflict during takeoff roll and executing an uneventful rejected takeoff due to a taxiing aircraft crossing the runway.