One of the world's largest data centres has opened for business in the UK, protected by bomb-proof glass and powered by enough electricity to run a small city.

The NGD Europe data centre, just outside Newport in south Wales, has 750,000 square feet (70,000 square metres) of floor space, or enough to house about 19,000 server racks. It officially opened on Monday, and its operator hopes to sign up big customers that need to run busy websites and other computing services.

The owner, Next Generation Data, invested about £200 million to convert a former chip manufacturing plant on the site that never opened for business. The first two tenants, BT and Logica, started moving equipment in last month and have signed long-term contracts worth a combined £20 million, Next Generation Data said.

The site has its own substation providing 90 megavolt-amperes of electrical power, or enough to supply a city of 400,000 people, the company said. To guard against terrorism and other attacks it has "triple-skinned walls, bomb-proof glass, prison-grade perimeter fencing, infra-red detection, biometric recognition and ex-special forces security guards".

Few data centres are bigger than about 200,000 square feet, although Google and some other large companies have built massive facilities from which to run their services. Microsoft's new data centre near Chicago, for example, occupies 700,000 square feet and is its biggest yet, the company has said.

NGD Europe is a tier-three facility, which specifies a high level of redundancy under the Uptime Institute's data centre tiering system, though not the highest. The site was chosen because of the power supply and its proximity to local carrier exchanges, and becauseof easy links to London.

Next Generation Data says it uses fresh air cooling and Energy Star equipment throughout to help reduce its environmental impact. It offers managed and colocation services, and data center "suites" starting from 3,000 square feet that have their own universal power supplies.