More than 100,000 people packed into the world's largest cricket stadium in Modi's home state to give Trump the biggest rally crowd of his political career.

The event was the pinnacle of the day's enviable trio of presidential photo-ops, sandwiched between Trump visits to a former home of independence leader Mohandas Gandhi and a planned tour of the famed Taj Mahal.

Nearly everyone in the newly constructed stadium in Ahmedabad in western India sported a white cap with the name of the event, "Namaste, Trump" or "Welcome, Trump".

Embarking on a whirlwind 36-hour visit, Trump opened his speech by declaring that he had come to deliver the message that "America loves India, America respects India and America will always be faithful and loyal friends to the Indian people."

The boisterous scene featured musicians on camels and a musical medley of Bollywood hits and Trump's campaign rally playlist, including numerous Elton John songs that seemed to puzzle most of the crowd.

While some of his foreign trips have featured massive protests and icy handshakes from world leaders, in India he instead received a warm embrace from the ideologically aligned and noted hugger Modi.

In Ahmedabad hundreds of billboards featured the president and first lady Melania Trump and thousands lined their motorcade route.

His first stop was Gandhi's home, where Trump donned a prayer shawl and removed his shoes to inspect the spinning wheel used by the famed pacifist.

Tens of thousands of police officers were on hand to keep security tight and a new wall has come up in front of a slum, apparently to hide it from presidential passers-by.

The cricket stadium was packed with revellers, many of whom sported Trump and Modi masks, as they sat in searing heat. Scores of attendees streamed out before Trump finished his 27-minute speech.

Trump lavished praise on both Modi and the democracy he leads, touting an effort to lift residents out of extreme poverty, saying "India gives hope to all of humanity."

"The story of the Indian nation is a tale of astounding progress," Trump said. "Today I say to every Indian, north and south ... take pride in the glories of your past. unite for an even brighter future and let our two nations always stand together as powerful defenders of peace and liberty."

Trump and the first lady were to visit the Taj Mahal, the immense white marble mausoleum built in Agra in the 17th century.

The visit comes at a crucial moment for Modi, a fellow populist, who has provided over a steep economic downturn and unfulfilled campaign promises about job creation.

The president will conclude his whirlwind visit to India on Tuesday with a day in the capital New Delhi, including meetings with Modi over stalled trade talks and a gala dinner.

The two nations are closely allied, in part to act as a bulwark against the rising influence of China. Trump announced at the stadium that India would soon buy $US3 billion of American military equipment.

Trade tensions between the two countries have escalated since the Trump administration imposed tariffs on steel and aluminium from India. India responded with higher penalties on agricultural goods and restrictions on US medical devices. The US retaliated by removing India from a decades-old preferential trade program.

Alluding to tense trade negotiations, Trump voiced optimism that a deal could be reached but also lightheartedly told the rally crowd about Modi: "Everybody loves him, but I will tell you this. He's very tough."

Australian Associated Press