The RIBA-organised competition aims to transform the historical area - which council bosses believe has a 'fractured spatial character' - into a 'high-quality contemporary city square'.
The winning design must respond to the scheme's brief, which demands that the square is transformed into as 'a dynamic, inspirational city square that people will love and use'.
A shortlist of up to six schemes will be selected from the open first stage. An honoraria of £2,000 will be paid to each team reaching this stage of the process, with £5,000 paid to the winner. The deadline for the submission of design ideas is 26 April.