The owner of four new tourist buses which have been damaged by vandals has described the incident as a “pre-meditated attack on the tourism industry in Belfast”.

The incident is thought to have occurred between 6.30pm and 10.30pm on Sunday at a depot at Longlands Avenue in Newtownabbey.

The vandals gained access to the depot by using sledgehammers to break through a concrete wall. Once inside they smashed 13 windows, damaged bodywork and sprayed fire extinguishers into the electrics of all four open-top vehicles, which are owned by Belfast City Sightseeing.

The intruders also forced entry into office premises, breaking a window and two mirrors, and police believe an attempt was made to steal a Land Rover parked at the depot.

Neighbours alerted police to the incident after the alarm systems onboard the buses were activated by the attack.

The buses, which were purchased in January at a cost of £50,000 each, had only been in operation for a matter of days.

Robert Wilson, director of Belfast City Sightseeing, said: “There is a strong possibility that they will have to be returned to London for repair.

“At the moment we estimate the cost to be about £10,000, but once the fleet have been fully examined this may multiply by a number of times.”

The buses had been planned to service the city over the busy Easter break.

A back-up fleet is being sent in the hope of resuming a skeleton service by Wednesday and normal service within a week. However, Mr Wilson said the issue was much wider than this.

“We had people due in today for interviews as drivers and tour guides over Easter and I have had to send them home.

“This is more than just mindless vandalism — it is a deliberate and pre-meditated attack on a business and on the tourism industry in Belfast.”

The Mayor of Newtownabbey, John Scott, said: “I am absolutely disgusted to hear about this attack on the Belfast City Sightseeing buses. In the wake of the attack on the young policewoman it gives our borough a terrible image and overshadows all the positive things that are going on here.

“Newtownabbey and Northern Ireland are trying hard to promote tourism and when things like this happen it is just a disgrace. I don’t know what people are thinking.”

A police spokesman said: “The PSNI condemns any incidents such as this, where property is mindlessly damaged at someone else's expense. Those who caused this damage have shown a complete disregard for the property of others.”

Anyone with information about the incident is asked to contact police on 0845 600 8000.