Tens of thousands of fans were ordered from the 75,600 capacity stadium when the alert was sounded about 20 minutes before the scheduled 1400 GMT kickoff.
The game ‘has been abandoned, fans are leaving the ground. Please avoid the area if possible,’ Manchester police said on their Twitter account.
United confirmed that a security alert caused the abrupt cancellation.
‘Due to the discovery of a suspect package in the North-West Quadrant of the ground, the match with Bournemouth been abandoned today on police advice,’ a United spokesman said in a statement.
Inside the stadium, announcements were made on the public address system that security staff should invoke ‘operation red code’.
Half of the stands at Old Trafford were evacuated. United said the suspec package had been discovered in the Stretford End stand.
Public address announcements instructed supporters in the South and East Stands -- including travelling Bournemouth fans -- to remain in their seats before the game was called off.
It is the second time in less than a week that Manchester United have been involved in a security alert.
Their game at West Ham United on Monday was delayed after their team bus was attacked by fans.
Louis van Gaal's side went into the game seeking a victory that would leave them in fourth place -- and qualified for next season's Champions League -- should local rivals Manchester City fail to win at Swansea.
There was no initial indication of the seriousness of the incident but by the scheduled 3:00pm kick-off, stewards outside the ground were telling supporters that the game had been abandoned and, within minutes, the decision was confirmed by police.
People who remained inside the stadium were told to stay in their seats ‘while the forecourt is cleared of fans already evacuated from the stadium.’
The club held up announcing the decision to fans remaining in two other stands for another 10 minutes, to avoid congestion outside the ground. By 3.15pm remaining parts of Old Trafford were evacuated.
