Unable to buy beer seven minutes after the cut-off time for retail shops, a man violently assaulted an employee at a 7-Eleven store in Changi Village.

The vicious attack last Thursday, which a witness said went on for half a minute, left the 43-year-old male employee with blood streaming down his face and a blood-spattered work polo shirt.

The witness, Mr Muhammad Firdaus Ahmad Fauzi, who first wrote in to Stomp, said there was also blood on the walls.

The employee, who had been alone in the store at that time, contacted the police and called for his own ambulance.

Under the law, retail shops are not allowed to sell takeaway alcohol from 10.30pm to 7am. Drinking is also banned in all public places from 10.30pm to 7am.

Mr Firdaus, who had been buying dinner during a work break with a friend, said the attack was very sudden. "The employee shouted for help and also banged on the store's glass front from the inside," said the 27-year-old safety coordinator. "We talked to the employee after the attack and asked if he needed aid. The ambulance came shortly after."

A 7-Eleven spokesman said the company is "aware" of the incident, which took place at 10.37pm.

He added that all cabinets containing alcohol are locked in accordance with the retail sales restrictions under the Liquor Control (Supply and Consumption) Act.

The spokesman said the victim was sent to Changi Hospital, where he received outpatient treatment.

"He is currently on medical leave and recovering at home. The 7-Eleven team has visited him and will continue to provide all necessary assistance to him and his family. We are also cooperating fully with the police in their investigations," said the spokesman.

The police said they were alerted to the incident at 10.29pm that night and that investigations are ongoing.

Correction note: An earlier version of the story wrongly stated the time that police were alerted to the incident.