Five people were injured as a suspected pipe bomb exploded on an overpass near an Istanbul metro station in Istanbul’s Bayrampasa on Tuesday, according to the head of the district.

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The head of the Bayrampasa district, Atilla Aydiner, spoke live on A-Haber television soon after the incident Tuesday.

"Five of our citizens were injured when a pipe bomb left on barriers on the overpass exploded," Aydiner said.

There were conflicting reports about the number of casualties. Earlier, local media reported that one person was killed in the blast and another six people injured.

#Bayrampasa Metro explosion heard around 17:30 local time in Istanbul, Turkey. — Harry Fear (@harryfear) December 1, 2015

Initial reports suggested that the explosion was caused by a power transformer blowing up.

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.

Kirazlı metrosu bayrampaşa civarında bi patlama sesi ile metro durdu yolcular indi ve yürüyorlar @trthaberpic.twitter.com/QIEkXVPZqU — Beyoglu İlce Mem (@beyogluilcemem) December 1, 2015

Bayrampaşa Metrosu civarında bir çok araç hasar görmüş.. Patlama nerde oldu ne oldu bilen yok.. pic.twitter.com/bebtXP7ZgM — ✦ T.☪ BAHA T.☪ ✦ (@ELTURC_O) December 1, 2015

#İstanbul: #Bayrampaşa Metro istasyonu yakınında gerçekleşen patlamada can kaybı olmadığı, 1 yaralı olduğu açıklandı pic.twitter.com/5DduZaD0ur — İstanbul Indymedia (@Istanbul_Indy) December 1, 2015

The explosion was heard in several districts of Istanbul, residents of the city said on Twitter. Local media reported that fire services and ambulances were sent to the site of the incident.

Suan icin trafo oldugu soyleniyor ve kesin olmamakla birlikte 1 ölü 1 yarali oldugunu soylediler pic.twitter.com/CdXjf1U3D2 — Onur Düğenci (@onurdugenci) December 1, 2015

Electricity was cut off in Bayrampasa and the surrounding district, according to HaberTürk TV.

Istanbul police said that the cause of the blast is still unknown, adding that an investigation into the incident has been launched, Reuters reported.

Bayrampasa is a suburban district located on the European side of Istanbul comprised of residential and industrial areas.

Turkey has been on alert since over 100 people were killed in two suicide blasts in Ankara in October. The terrorist attack was blamed on Islamic state militants. Turkey, a NATO member state, has been taking part in the US-led campaign against terrorists in the region.

READ MORE: Turkey foiled major ‘Paris-style’ attack in Istanbul – reports

The Kurdistan Workers Party (PKK), which has been fighting Ankara for autonomy in Turkey’s mainly Kurdish southeast, has carried out carried out bombings in Istanbul in the past. Among the latest, PKK claimed responsibility for the bombing of an Istanbul police station which killed four on August 11.