Authorities said that a south Asian militant group with links to al-Qaeda had admitted carrying out the attack using a bomb placed in a briefcase.
The device left a crater three to four feet deep near the main reception area of the high court, where lawyers and visitors collected entry passes.
An estimated 120 soldiers, police and bomb squad specialists arrived at the scene soon afterwards.
Indian authorities received an email claiming responsibility for the attack from the south Asian militant group Harkat-ul-Jihad Islami (HUJI), which has bases in Pakistan and Bangladesh and is linked to al-Qaeda.
“That mail has to be looked at very seriously because HUJI is a very prominent terrorist group among whose targets India is one,” SC Sinha, director general of India’s National Investigation Agency, told reporters.
India’s prime minister, Manmohan Singh, is currently on an official visit to Bangladesh. “This is a cowardly act of a terrorist nature, but we will deal with it. We will never succumb to the pressure of terrorism,” he told reporters in Dhaka.
In London, the Foreign Office issued a statement saying: “The UK is committed to standing together with India in the fight against terrorism in all its forms and we will continue to work together to counter this threat.”