A Stagecoach Manchester spokesperson said: "Our hearts go out to all of those affected by the terrible events in Manchester last night.
"The safety and security of our customers and employees is our absolute priority. We have extensive measures in place across our transport services to ensure people can travel with us in confidence.
"In addition to the response of the emergency services, we would like to pay tribute to many of our staff who returned to work or stayed on after their shift last night to assist our efforts in diverting services to help take people to a place of safety, and to take some of those who were injured to hospital.
"This morning we have as many buses operating as possible, including all of our reserve fleet, to help provide replacement services in the areas where trains and trams are not currently able to run.
"Our teams are being extra vigilant in light of recent events and we would also encourage customers and members of the public report to anything suspicious. As always we will liaise closely with the police and other authorities and take their advice on any further measures required."