US President Donald Trump has promised "an incredible trade deal" and "the most feared military equipment on the planet" at a rally organised for him India.

More than 100,000 people attended the event at the opening of the world's biggest cricket stadium.

Indians wore cardboard Trump masks and "Namaste Trump" hats to welcome the US President at the new Motera stadium in Prime Minister Narendra Modi's own political homeland, the western city of Ahmedabad.

Mr Modi, a nationalist who won re-election last year and has shifted his country firmly to the right with policies that his critics decry as authoritarian and ethnically divisive, touts his relationship with Mr Trump as proof of his own global standing.

US officials have described Mr Trump's visit as a way to counter China's rise as a superpower.

"You have done a great honour to our country. We will remember you forever, from this day onwards India will always hold a special place in our hearts," Mr Trump said to thunderous applause.

India is one of the few big countries in world where Mr Trump's personal approval rating is above 50%.

It has built up ties with the United States in recent years as Washington's relationship has become strained with India's foe Pakistan.

"As we continue to build our defence cooperation, the United States looks forward to providing India with some of the be stand most feared military equipment on the planet," Mr Trump said.

Mr Trump said the two countries will sign deals to sell military helicopter deals worth $3 billion.

He also said that the US must become the premier defence partner of India, which relied on Russian equipment since the Cold War.

Mr Trump visited the Taj Mahal in Agra and held official meetings in Delhi during his trip.

Folk dancers carrying colourful umbrellas danced alongside the red carpet as drummers, trumpeters and other musicians performed on the airport grounds to welcome Mr Trump and the US delegation.

The two sides did not manage to hammer out a trade deal ahead of the visit, with differences remaining over agriculture, medical devices, digital trade and proposed new tariffs.

Mr Trump said he was going to discuss economic ties with Mr Modi, describing him as a tough negotiator.

"We will be making very, very major, among the biggest ever made, trade deals. We are in the early stages of discussion for an incredible trade agreement to reduce barriers of investment between the United States and India," he said.

Last year, Mr Trump held a "Howdy Modi" rally with Mr Modi in Houston, drawing 50,000 people, mainly Indian Americans. At the time, Mr Trump likened Mr Modi to Elvis Presley as a draw for crowds.

Mr Trump's entourage includes daughter Ivanka and son-in-law Jared Kushner, as well as members of his cabinet, including Commerce Secretary Wilbur Ross.