Shortly before 3 pm local time on Friday, a lorry drove into a crowd of people on the pedestrian street Drottninggatan. At least three people are reported dead, and eight injured.
Swedish security police Säpo and Prime Minister Stefan Löfven describe it as a terrorist attack.
The ministry and the Finnish Embassy in Stockholm are closely monitoring the situation. The embassy is about 3 km from the scene of the crash at the Åhléns department store.
According to the Dagens Nyheter website, the lorry slammed into the store's perfume section. An eyewitness says the truck, belonging to a brewery company and hijacked earlier, was driving at high speed of "probably 100 km per hour". Police received the first alarm at 2.53 pm. Shots were heard near Åhléns and around Hötorget square.
The city's metro system was shut down, and bus service halted in the city centre.
No word on Finnish casualties
Foreign Ministry spokesman Harri Kilpi says those close to the site should notify someone that they are safe.
"If you were near the scene, then inform your relatives that you are all right," Kilpi advises.
The ministry also calls on Finnish citizens nearby to file a travel notification online or a Facebook Safety Check.
Kilpi told Yle in the late afternoon that the ministry did not have information as to whether there was still a threat in the area. There is no word yet of any Finnish casualties. Thousands of Finns live in and around the Swedish capital.
Shortly after 5.30pm, the Foreign Ministry said that there were numerous Finns within an area sealed off by police, and that contact had not been made with all of them. There was no word of any injured Finns.