Lyttelton Harbour will be working a little differently this weekend, as SailGP takes to the water

The world's biggest ticketed sailing regatta is expecting to draw 22-thousand spectators.

Environment Canterbury Harbourmaster Guy Harris says they've declared it a major maritime event.

He says there'll be no shipping in the afternoons from today, and those watching from the water must follow the rules.

Harris says they need to stick to the five knot limit, and obey any instructions around where and where not to anchor, as there is critical infrastructure on the seabed.