A group of people from an unmarked van wearing gas masks have entered the Thames Water Swindon office on Kembrey Business Park.

The office building has been locked down for over an hour, as police say they are attending a 'suspicious incident'.

It is unclear what the nature of this incident is, but over 10 emergency vehicles are in attendance, including the police, ambulance and fire service.

LIVE UPDATES: Thames Water office evacuated

Thames Water employees trapped in the building say they have been given no information, but one anonymous employee told this newspaper that "they haven't evacuated us yet."

"Nobody is allowed in or out," he told The Adver.

Although police officers have not yet confirmed the nature of the incident, emergency responders appear to need gas masks in order to enter the building.

"We are working alongside the local fire brigade and police following an incident at our Walnut Court office this morning," said a spokesperson for Swindon Police.

"The health and safety of our employees is our top priority and we are taking precautionary measures to support staff who have been impacted by this.”

Rumours have been spreading among workers on the business park who believe there may be a 'suspicious package' involved, but Thames Water and Swindon Police have not yet confirmed or denied this.