The site is set to become the largest offshore project in the world, almost doubling the current record holder, London Array (630MW). It is due online in 2020.
Dong has made a "multi-billion pound investment" in the project, the largest ever made by the developer, a spokesman said. However, the company however declined to give an exact investment figure.
Hornsea 1 is located 120km off the England's east coast on a covering 407 square kilometres, Dong said. The project area is larger than Malta (316 square kilometres).
It is positioned near two other Dong projects, the operating Westermost Rough and Race Bank, currently under construction.
A total of 171 Siemens 7MW turbines will be installed at the site, with the blades produced at the German manufacturer's new facility in Hull, north-east England. Siemens was named preferred supplier in July 2015.
Dong CEO Henrik Poulsen said the project would "push the boundaries" in offshore wind.
RenewableUK deputy chief executive Maf Smith said: "Its size is guaranteed to bring a multitude of benefits to the UK, in particular, a huge amount of inward investment and the creation of local jobs on the east coast of England."
Hornsea 1 was one of five projects to receive a final investment decision-enabling contract for difference subsidy deal from the UK government in April 2014. The deal offers Dong a fixed tariff for the electricity produced.
In February 2015, Dong acquired the development rights to Hornsea 1 from the Smart Wind consortium for an undisclosed fee.
Dong owned a 33% stake in the consortium at the time. The developer then went on to buy the entire Hornsea Zone from the other Smart Wind partners Mainstream Renewable Power and Siemens Financial Services.
In October 2015, Dong made a final investment decision on the 660MW Walney Extension project off the UK's east coast. The eastern phase of Walney Extension will also feature Siemens' 7MW turbine. The western phase will use MHI-Vestas' V164 8MW turbine.
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