Representatives in churches across Nice have expressed their shock and outrage at last night's apparent terrorist attack on the city, when a man drove a heavy truck into Bastille Day fireworks celebrations, killing more than 80 people.

While the city remains in lock-down, priests and chaplains were this morning preparing for special prayer services to remember the victims and their families.

Fr. Peter Jackson, the chaplain of Holy Trinity Anglican church on Rue de la Buffa, was at the Bastille Day fireworks on the Promenade des Anglais last night. He described a "convivial, patriotic atmosphere" before the attack. It was not until he got home and heard the sirens "through the night" and began looking at social media that he realised what had happened.

Jackson told Christian Today: "It leaves you quite bewildered. It is unbelievable that this has happened, atrocities just around the block. I am waiting to see who needs us. I don't know if any Brits were killed or injured. There will be people who need visits in hospital."

Jackson said that one of his church wardens had dodged the truck last night, but she was too shaken to speak to the media.

Holy Trinity typically attracts a congregation of 80-100 on Sundays but Jackson is expecting more this weekend. "This is a historic English speaking gathering place," he said. "I will be changing what we do in church to enable people to pray for the families."

He added: "This is very shocking for France. This is obviously not the first time and on this huge scale. This (Nice) is a place where, apart from Paris, people come. We had got used to army presence for months because of the terror alert following last year's attacks. But it is still a massive shock. How do you stop an individual who is prepared to do that? It is shocking. To be at this very French gathering, where everyone was very relaxed – it's just horrible to think that everything can be shattered. I remember the London 7/7 bombings and I was in Washington on (the New York attacks of) 9/11, and now this."

At Nice's main Catholic Cathedral, St. Reparate on Place Rossetti, Fr. Sylvain Breison echoed the sense of devestation. "We are very shocked. There is a lot of sadness. Today, we try to revive, and organise the welcome for people who want to pray and come and talk in these terrible moments," he said.

Asked if many people were coming to pray, Breison said, "A little this morning – because the whole city has been locked down by the police. And people are very shocked. But we are expecting more people later in the day."

On suspicions of terrorism, Breison said, "We are not sure. The Government says it is terrorism but we don't know from where. It seems to be a man who was alone but we don't know for sure."

Dr Paul Cooke of the evangelical France Mission Trust said: "I was really shocked to hear the news. It is particularly sad given that France has had such terrible attacks recently. And there was a mood of optimism lately, after the European Championships even though France lost in the final. There has been a lot of activity from Christians in France, praying, expressing shock and grief, using the hashtag 'PrayForNice' on Twitter. People are just remembering the population and families of the victims. As things develop it is important for people to build bridges where they can and not fall into the trap of tarring all members of one community with the same brush and not deepen divisions further."

At IBC international evangelical church on Rue Vernier, pastor James Arnold said that Christians are coordinating across the city. "Last night was about just trying to find our people and make sure everyone was OK. Once that passed we woke up this morning to a load of messages from churches all round the world, some we had never heard of. It is very encouraging. We have 58 kids here at the moment for Kids Camp and it is their last day. We had an impromptu prayer service with the parents as they were dropping off the kids this morning. Many of them were non-believers. And now we are looking at what we will do with other churches in Nice. We will hold another prayer service this evening."

Arnold added: "On the one hand, our lives continue, and on the other side there is this huge tragedy to deal with."