The exact cause of a car explosion that killed at least eight people in India's capital is still being investigated as the rest of the country remains on high security alert, local media is reporting.
Twenty people have been injured in the explosion, which took place in the historic Red Fort in densely populated Delhi.
Here's what we know.
What happened?
Just before 7pm, local time, a blast occurred near the gates of Red Fort Metro station.
It is believed to have come from a Hyundai i20 car stopped at a traffic signal, Home Minister Amit Shah told local media.
"A slow-moving vehicle stopped at a red light. An explosion happened in that vehicle, and due to the explosion, nearby vehicles were also damaged," Delhi Police Commissioner Satish Golcha told reporters.
The explosion triggered a fire that damaged several other cars and rickshaws parked nearby.
At least eight people were killed and 20 people are being treated for injuries at a government hospital.
Photos from the scene show shattered windows and mangled parts of vehicles, while plumes of fire and smoke billow from the burning cars.
A witness who lived close to the scene told AP he was at home when he heard a loud explosion.
"I rushed out with my children and saw several vehicles on fire, body parts all over," Om Prakash Gupta said.
What have investigators said?
The National Investigation Agency, India's federal anti-terror agency, is probing the cause of the blast.
Home Minister Amit Shah said CCTV footage from cameras in the area would form part of the investigation.
"We are exploring all possibilities and will conduct a thorough investigation, taking all possibilities into account," Shah said.
"All options will be investigated immediately, and we will present the results to the public."
Indian Prime Minister Narendra Modi offered his condolences on social media.
"Condolences to those who have lost their loved ones in the blast in Delhi earlier this evening," he wrote.
"May the injured recover at the earliest."
What did witnesses see?
Witnesses who spoke to Reuters described hearing a loud explosion.
"I was at the metro station, going down the stairs, when I heard an explosion. I turned around and saw a fire. People started running helter-skelter," one woman, Suman Mishra, said.
Wali Ur Rehman said he was sitting in his shop.
"I fell from the impact of the explosion, it was that intense," he told news agency ANI.
An ambulance driver told Reuters what the scene looked like as emergency services arrived.
"The bodies were in parts and we had to pick different parts and bring them back in the ambulances and later brought them to the hospital," the driver said.
Are there security concerns for travellers?
Major train stations across India, financial capital Mumbai and the state of Uttar Pradesh, which borders Delhi, were all put on high alert.
The US Embassy in Delhi issued a security alert to its citizens, asking them to avoid crowds and areas surrounding the Red Fort and to stay alert in places frequented by tourists.
Australia's government travel advice website Smart Traveller has been updated to acknowledge the explosion.
"lf you're in the area, follow advice from local authorities and monitor local media," it read.
What is the Red Fort?
The Red Fort, known locally as Lal Qila, is a major tourist attraction in the Old Delhi section of the city.
A former imperial palace, the Red Fort complex is a UNESCO World Heritage site known for its Mogul architecture, which flourished in India in the mid-16th century.
The structure was built by Shan Jahan in 1526 AD and is a fusion of Islamic, Persian, Timurid and Hindu traditions.
It is one of the largest monuments in the city and attracts thousands of visitors annually.
The prime minister addresses the nation from the fort's ramparts every year on August 15, India's Independence Day.
Has Delhi experienced bombings before?
The Red Fort was the site of a terrorist attack on December 22, 2000, when two soldiers and a civilian were murdered.
The attack was carried out by two Lashkar-e-Taiba militants, who began firing indiscriminately.
Lashkar-e-Taiba is a Pakistani militant group.
In June that year, two people, including an eight-year-old girl, were killed and about a dozen others were injured in two powerful bomb blasts near the Red Fort.
Delhi was the target of blasts during the 1980s and 1990s, with public places such as bus stations and crowded market areas hit in attacks blamed on Islamist militants or on separatists from the northern Sikh state of Punjab.
About a dozen people were killed in a briefcase explosion outside the Delhi High Court in 2011 — the last such major incident in the city.
Security in the national capital is the responsibility of the federal home ministry. Delhi police report directly to it, though the capital territory also has its own local government.
ABC/Wires
