A Scots tourist has described the moment a lorry ploughed into busy Berlin Christmas market in a suspected terror attack killing 12 people.

Thomas Butler, from Uddingston in South Lanarkshire, had only touched down in Germany three hours earlier with his girlfriend specifically to visit the city's famous markets in the lead up to Christmas.

The ScotRail worker said they were just leaving the market area to go for dinner when he saw a lorry speeding into the crowd at the Breitscheidplatz public square on Monday evening.

Berlin Police said on Twitter on Tuesday morning that the incident was intentional and a suspected act of terrorism.

He said: "We had literally put our stuff in the hotel room and went to the Christmas market here.

"We had done a bit of shopping and were on our way for something to eat.

"Before we knew it there was this big commotion. We could see the tail end of this quite large arctic lorry passing me."

He continued: "It turned the corner, it went out of my eye shot and we heard all this noise.

"Before I knew it everybody was screaming. All you heard was this big loud noise banging."

Just moments after impact, hundreds of panicked people began running in Thomas' direction.

Mr Butler added: "We just assumed the worst. I grabbed my partner, Jen, and rather than running in the same direction as everyone else, we decided to run down the stairs to the subway station.

"I went down to the subway station and a train had just pulled in, there must have been 20 or 30 people getting off the train.

"Panic just set in and I'm shouting at them, 'don't go upstairs, somethings happened up there'.

"Someone was translating for me. Then a man ran up the stairs and ran back down and told everyone to get back on the train."

The 30-year-old, who works as a train ticket inspector, is currently stuck behind police cordons in the Waldorf Astoria hotel, which is being used as a crisis centre.

He says he is surrounded by victims' families and other people caught up in the incident, which police are treating as suspicious.

Mr Butler said: "One police officer said it was a road traffic accident but it's quite clear that's not what it was.

"Everyone on the ground is pretty certain it's a terrorist incident.

"It's quite clear the route they took through the Christmas market and the pace that they were going, it's definitely a terrorist incident.

"We're pretty shook up. We're OK now but at the time it was very, very scary."

He added: "People surrounding us in the crisis centre here are victims' families and they are distraught.

"There's people been lost tonight. We've just been very lucky we were not in the wrong place.

"It could have been a lot worse for us."

The incident took place at a market outside the Kaiser Wilhelm Memorial Church on Monday evening.

Images shared on social media showed a damaged black truck with a smashed windscreen and debris at the scene.

Authorities said a "suspicious person" had been arrested near the scene and a passenger died "on the spot".

Thomas Neundorf, a spokesman for the Berlin Police, said 50 people had been injured.

"According to what we've been able to ascertain, a lorry drove into the Christmas market," he said.

"This lorry came from Kantstrasse. It went through the market stalls and then it left the area towards Budapesterstrasse.

"Multiple persons were injured by the lorry. According to the limited information we have, we have to report nine deaths including the passenger of the lorry."

He added: "The driver of the lorry fled. We were able to arrest a suspicious person nearby.

"Now we are checking if this is the driver of the lorry."

In response to whether or not the incident was an accident or an attack, Mr Neundorf said it was unclear.

"The background to this incident is not yet clear," he said.

"The criminal police of the state of Berlin is currently investigating.

"All we can say at this current point in time is that there is no more danger.

"We are investigating how this lorry came to drive into the Christmas market, how did this situation happen?"

Dozens of emergency services were at the scene of the incident

A Foreign Office spokesman said: "We are urgently investigating reports of an incident near the Kaiser Wilhelm Memorial Church in Berlin and are in close contact with local authorities."