The blast near a gate at the High Court, the second at the building in five months, came despite a high alert in the city. It renewed doubts about India's ability to protect even its most important institutions despite a security overhaul that followed the 2008 Mumbai siege.
"There was smoke everywhere. People were running. People were shouting. There was blood everywhere. It was very, very scary," said Sangeeta Sondhi, a lawyer, who was parking her car near the gate when the bomb exploded.
A Muslim militant group claimed responsibility for the blast in an email, but investigators said it was too early to name any group as suspects. The government rallied Indians to remain defiant in the face of such attacks.
"We will never succumb to the pressure of terrorists," Prime Minister Manmohan Singh said during a visit to neighboring Bangladesh. "This is a long war in which all political parties and all the people of India will have to stand united so that this scourge of terrorism is crushed."
The bomb exploded about 10:14 a.m. near a line of more than 100 people waiting at a reception counter for passes to enter the court building to have their cases heard.
The High Court is an appeals panel below India's Supreme Court. On May 25, a small explosion that appeared to be a failed car bomb erupted in the court's parking lot.
The latest blast shook the courthouse, sending lawyers and judges fleeing outside, said Sanjiv Narula, a lawyer who was in the building.
People ran to the blast site to assist the injured, piling them into auto-rickshaws to take them to the hospital. Officials said the blast killed 11 people and wounded 59 others. Ambulances and forensic teams rushed to the scene, along with sniffer dogs and a bomb disposal unit, apparently checking for any further explosives.
Renu Sehgal, a 42-year-old housewife with a case before the court, had just received her pass and was standing nearby with her uncle and mother while her husband parked their car when she heard the explosion.
"The sound was so huge and suddenly people started running," she said. "We were all in such a big panic. ... I'm lucky I survived."
The court building was evacuated after the attack.
The blast probe was quickly turned over to the National Investigation Agency, which was set up after the Mumbai siege to investigate and prevent terror attacks.
"We are determined to track down the perpetrators of this horrific crime and bring them to justice," Home Minister Palaniappan Chidambaram told Parliament.
An email sent to several TV news channels claimed the bombing on behalf of Harkat-ul-Jihad-al-Islami, an Islamic extremist group said to be based in Pakistan that was blamed for numerous terror strikes in India.
"We cannot say anything about the email until we have investigated it thoroughly," NIA chief S.C. Sinha said. "At this point the investigation is fully open and it's not possible to name any group."
The court bombing was the first major terror attack in India since a series of blasts in three busy Mumbai neighborhoods killed 26 people on July 13. Suspicion for those attacks fell on the shadowy extremist network known as the Indian Mujahedeen, though no one has been arrested.
The bombers struck the court even though the capital had been on high alert because Parliament was in session and because of the previous blast at the court building.
Ravi Shankar Prasad, a spokesman for the opposition Bharatiya Janata Party, faulted the government for not preventing such an attack outside a top court in the heart of the capital.
"This blast happens and there is no proper security, no intelligence pick up. A terrorist comes with impunity," he said. "How many more innocent Indians will have to be killed?"
However, police official Dharmendra Kumar said the court building itself was strongly protected by police. The explosion hit near a busy main road that is difficult to police outside the court building.
The attack rekindled memories of the string of deadly bombings that rocked the country in 2008. But that violence had mostly abated after the November 2008 siege of Mumbai, when 10 Pakistan-based militants wreaked havoc across India's commercial capital for 60 hours, killing 166 people.
However, a series of smaller attacks raised concerns in recent months that the violence was returning.
Last Sept. 19, two gunmen on a motorcycle shot and wounded two Taiwanese men outside a famous New Delhi mosque. A few minutes later, a bomb rigged to a nearby car malfunctioned and caught fire. On Dec. 7, a bomb exploded in the city of Varanasi, killing a 2-year-old, and a few months later came the failed attack on the High Court in New Delhi.
Some analysts feared these attacks, culminating in the July attack in Mumbai, signaled an effort to regroup by the Indian Mujahedeen -- a domestic militant group blamed for many of the 2008 attacks.