The Indian capital faces possible "imminent" militant attacks, the United States, Australia and Britain warned on Saturday, stepping up their risk advisories to travellers to New Delhi.
New Zealand also warned of an "extreme risk" of terrorism in India as the nation battles to reassure visitors it can safely host the Commonwealth Games in October in New Delhi, which has been targeted before by militants.
"There are increased indications that terrorists are planning imminent attacks in New Delhi," the US embassy said in a statement on its website, urging tourists to avoid half-a-dozen of the city's popular shopping areas.
Police in New Delhi were taking "appropriate measures" in response to the warnings, said police spokesman Rajan Bhagat as a source said police had been put on alert.
"Security is adequate," Ravindra Singh, spokesman for India's Ministry of Home Affairs, said.
India is home to a wide range of separatists and insurgents, but Islamist terror groups, both homegrown and from across the border in Pakistan, are considered the most dangerous threat.
Tighter security was already in place around the city's congested markets and tourist hotspots in response to earlier warnings by Western nations about the chance of attacks in New Delhi.
The latest warnings added the mention that attacks could be "imminent."
"Americans travelling or residing in India are strongly encouraged to maintain a high level of vigilance," the US embassy said in its notice.
Australia, Britain and New Zealand issued similar warnings.
The US advisory said markets in New Delhi such as Connaught Place in the heart of the city could "be especially attractive targets for terrorist groups."
"Specific and credible information indicates terrorist attacks in New Delhi, especially in markets, may be imminent," the Australian High Commission (embassy) said.
"New Zealanders are strongly advised to avoid market areas of New Delhi in coming days and weeks," New Zealand's advisory said.
The last major attack in New Delhi was a series of bomb blasts that ripped through busy, upmarket shopping areas in September 2008, leaving 22 people dead and wounding 100 more.
Security concerns about the forthcoming Commonwealth Games were stoked in April when two low-intensity bombs went off at a cricket stadium in the southern city of Bangalore ahead of an Indian Premier League match.
Some 8,000 athletes are expected to attend the Commonwealth Games.
India has vowed to provide "foolproof" security for athletes and spectators during the Games. The London-based Commonwealth Games Federation has said security for the Indian event is subject to "continual review."
In February, a bomb exploded in a packed restaurant popular with travellers in the western Indian city of Pune, killing 16 people, including five foreigners.
It marked the first major incident since the 2008 Mumbai attacks in which 10 Islamist gunmen launched an assault on multiple targets in India's financial capital, killing 166 people.
India blamed the Mumbai attacks on the banned Pakistan-based Islamist group Lashkar-e-Taiba, straining already tense diplomatic ties with its neighbour.
The run-up to the field hockey World Cup in February and March was overshadowed by concern some teams might pull out. Ultimately, the tournament went ahead without incident with a heavy police presence.