Last weekend’s attack at London Bridge was a “living nightmare”, the dean of Southwark Cathedral told his congregation on Sunday, the first day the church has opened since the bloodshed.

Hundreds of people packed the ancient edifice in the heart of the neighbourhood that had come under attack eight days earlier. “It’s lovely to hear the bells again,” one resident said.

Borough Market was still barricaded off to the public as police patrolled the streets and helicopters hovered overhead. Wellwishers added to the mounds of floral tributes left at the southern end of London Bridge.

Sunday’s choral eucharist was conducted by Christopher Chessun, the bishop of Southwark, with the sermon given by the dean, Andrew Nunn. Regular services have been held in local parish churches for the past week while police continued their forensic examination of the area.

Moments after the attack, police broke down the cathedral doors and smashed glass, Nunn said. The western door was boarded up and screened off. The door to the sacristy showed signs of the baton rounds police fired in their effort to gain access.

A church had been on the site of the cathedral for 1,400 years, Nunn said. “Those years have seen their share of war and pestilence and fire, but I doubt that ever before has the church been inaccessible to worshippers for a week, inaccessible as the place of peace and contemplation that people expect and need, inaccessible as the place of welcome and embracing, radical hospitality and love that we seek to be. But it happened.”

When he received news of the attack last Saturday night, he said: “I put on my dog collar and headed down Bankside to try and open up the cathedral so that we could be a place of refuge. But initially I didn’t get far.

“So I went through the back alleys … but heavily armed police barred my way and forced me back. ‘Run, run’ was all they shouted … [I] saw people lying on the pavement being cared for by the emergency services. ‘Run, run’ was all I could hear through the sound of sirens and helicopters.”

Despite the efforts of terrorists to divide people, Nunn said: “Difference does not mean division unless we choose to make it so, and we choose to make difference a blessing and an enrichment to our community, which is why we celebrate who you are, who we are, male and female, young and old, black and white, rich and poor, gay and straight – and I will say that again and again and again from this pulpit until it is deep in all our hearts, to the very core of our being.”

Chessun had begun the service by paying tribute to the emergency services and the local community. “Many more would have been killed and injured had it not been for the rapid and effective response from the police, and their engagement with people on the streets in recent days has been magnificent,” he said.

“The terror we have seen on our streets has been followed in recent days by many small acts of loving care for neighbours and many expressions of community solidarity. Londoners are determined to show that what has happened, terrible as it is, will not undermine the trust, friendships and goodwill which bind us together, and we celebrate our remarkable diversity, especially across different faiths, as a rich blessing.

Outside the cathedral, Alison Clark, a regular member of the congregation, said the service had been “a chance to reclaim the space against the background of so much evil, to say as a community we stand for loving one another. Hearing the bells ring out across Borough Market is a sign that good things can still happen.”

Thomas Smith and Marianne Boyle said they were delighted to see the cathedral reopened. “We’re getting married here in seven weeks, so it’s a special place for us,” said Smith. The couple’s marriage banns were read at the start of the service.

“The service was a chance to reflect on the past week. When you see the pubs you frequent and the church you attend so affected, it feels very close to home,” he added.