Around 20 minutes before the scheduled start of the game on Sunday between Manchester United and Bournemouth, a suspicious device was found in toilets inside England's second biggest soccer stadium, Xinhua news agency cited Manchester police as saying.
Though some players were already warming up on the pitch, spectators were taken out of the northwest section of the stadium once military bomb disposal experts rushed to the scene.
However, the "incredibly lifelike" explosive turned to be a security blunder.
"Following (Saturday's) controlled explosion, we have since found out that the item was a training device which had accidentally been left by a private company following a training exercise involving explosive search dogs," said assistant chief constable John O'Hare from Greater Manchester Police.
"While this item did not turn out to be a viable explosive, on appearance this device was as real as could be," he said, thus it was right to tell all the people, including players and match officials, to leave.
Half of the stadium, which has a capacity crowd of 75,600 people, was evacuated around 2.30 p.m. (local time). And a controlled explosion was carried out around 16.30 (local time).
Amid threats of terrorist attack hovering much of Europe, this incident added uneasiness for Britain. In fact, English soccer games have tightened security following last year's Paris attacks when the Stade de France was one target of bomb treat.
The security blunder at the most famous football venue aroused the anger of Tony Lloyd, the mayor and police and crime commissioner of Greater Manchester, for it not only brought economic loss and trouble to soccer fans but also exposed safety problems for the city.
"It is outrageous this situation arose and a full inquiry is required to urgently find out how this happened, why it happened and who will be held accountable," Lloyd said.
Some reports said the "lifelike" explosive device was left behind four days ago and discovered by an employee of the United club shortly before the game kick-off.
United executive vice chairman Ed Woodward said staff were regularly trained with the police and emergency services and the club will investigate the incident fully.
Whether the ticket-holders will be compensated or not is unclear yet as United have made no official comment on refunds for the moment.
The match has now been rearranged for the coming Tuesday.
On Wednesday, Britain raised the alarm level from Northern Ireland militants to "substantial", indicating a strong possibility of attacks on the mainland.
Furthermore, followers of the Islamic State hiding in Europe are also great concerns involving plots in Britain.