The home ministry has sounded a nationwide alert with special stress on four major cities - Delhi, Mumbai, Bangalore and Hyderabad - in wake of the blast in Varanasi.
"A general alert has been sent to all state governments and they have been asked to stay on high alert," Union Home Secretary G K Pillai said in New Delhi.
"It was low intensity blast which occurred at about 6.20 pm in which three-four people were injured. Subsequently we understand there could have been a stampede...as a result 15-20 people were injured. So roughly 20-25 people injured," he said.
According to home ministry sources, alerts have been issued to the four metropolis in particular.
They said a high-level team of the National Investigation Agency is also likely to visit the holy town.
Secretary for Internal Security at MHA, U K Bansal said, "We had alerted Uttar Pradesh Police sometime back. I am sure the UP police will take it as a challenge. There is no reason for panic."