A suicide bombing hit Istiklal boulevard, a main high street in the centre of Istanbul, just off Taksim Square, on Saturday.
According to media reports, including CNN Turk, two people were killed and several injured.
Emergency services were rushing to the area
The blast comes as Turkey is on edge, following a massive car bombing in Ankara last weekend which killed 37 people.
A similar attack last month in the capital left 30 dead, while 12 tourists were killed by a suicide bomber in Istanbul in January.