Lindt Cafe has reopened for business

Sydney's Lindt Cafe has reopened for business, three months after the deadly siege that claimed the lives of Tori Johnson and Katrina Dawson.

The cafe's doors officially reopened at 10am on Friday, about the same time a shotgun-wielding Man Monis ordered the doors locked shut on December 15 last year.

Monis proceeded to hold 18 staff and customers captive for 16 hours before the siege was ended in a hail of gunfire which claimed his life and the lives of Mr Johnson and Ms Dawson.

The cafe was packed on Friday as thousands turned up to pay tribute to Ms Dawson, Mr Johnson and staff.

Prime Minister Tony Abbott, Premier Mike Baird and NSW Opposition Leader Luke Foley each visited the shop on Friday to pay their respects.