Details added (first version posted on 20:17)
One person has been killed in an explosion near the subway in the Bayrampasa district of Istanbul, the Turkish media reported.
The head of the city district said that five people have been injured in the blast.
The explosion was caused by a bomb, the head of the Bayrampasa district said.
There are conflicting reports about the number of people injured. Turkish broadcaster NTV has reported that six people have been injured in an explosion of unknown origin.
Social media users have posted various photos of people evacuating the subway station, while local media said that trains have been stopped at one of the stations.
NTV also reported that the explosion may have been caused by a bomb on an overpass. According to other reports, the explosion was caused by a power transformer blowing up.
The explosion was heard in several districts of Istanbul, residents of the city tweeted. Local media reported that fire services and ambulances were sent to the site of the incident.
Electricity was cut off in Bayrampasa and the surrounding district.
Istanbul police said that the cause of the blast is still unknown, adding that an investigation into the incident has been launched.