US President Donald Trump will join Indian Prime Minister Narendra Modi at the mega 'Howdy, Modi!' diaspora event in Houston on Sunday to bolster Indo-US strategic ties, according to a White House announcement.

Modi on Monday hailed the announcement as a 'special gesture' signifying the special friendship between the two countries.

Emphasising the new bonhomie in the India-US ties under the Trump administration, this is for the first time in recent history that the leaders of the two largest democracies would be addressing a joint rally anywhere in the world.

More than 50,000 Indian-Americans from across the US have registered for the September 22 'Howdy, Modi! Shared Dreams, Bright Futures' event to be held at the NRG Stadium in Houston.

White House press secretary Stephanie Grisham said, 'It (Modi-Trump joint rally) will be a great opportunity to emphasise the strong ties between the people of the US and India, to reaffirm the strategic partnership between the world's oldest and largest democracies, and to discuss ways to deepen their energy and trade relationship.'

Hours after the White House announcement, Prime Minister Modi in a series of tweets said he is looking forward to joining the Indian origin community in welcoming Trump at the programme.

'A special gesture by @POTUS, signifying the special friendship between India and USA...highlights the strength of the relationship and recognition of the contribution of the Indian community to American society and economy,' the prime minister wrote on Twitter.

This would also be the first time that an American president would be addressing thousands of Indian-Americans at one place in the US.

India's Ambassador to the U Harsh Vardhan Shringla called Trump's participation in the 'Howdy, Modi!' event 'historic' and 'unprecedented.'

'It is reflective of the strong bonds of friendship and cooperation that has developed between India and the US,' Shringla told PTI.

The ambassador also said the two leaders addressing the event sets a bold precedent, which is unconventional and unique.

'It would be quite a historic meeting with Prime Minister Modi and President Trump jointly addressing over 50,000 Indian-Americans, mainly US citizens,' Shringla said.

White House officials told PTI that a request for the joint address was made by Modi to Trump when the two met in France last month on the sidelines of the G7 summit.

While India is not part of the G7 countries, Modi was invited as a special guest by French President Emmanuel Macron for the summit.

Trump, who enjoys a great chemistry and friendship with Modi, 'immediately accepted' the invitation to join him in Houston and directed his officials and secret service to make arrangements, officials said.

This would be the third meeting between the two leaders this year. The previous two were on the sidelines of the G20 Summit in June in Japan and in France in July on the sidelines of the G7 Summit.

In October 2016, Trump, then as the Republican presidential nominee, had addressed a strong crowd of some 5,000 Indian-Americans in New Jersey, a few weeks away from his historic win in the November 2016 elections.

So far, Trump is the only presidential candidate to address the Indian-Americans solely during an election year.

In his address, Trump had said that if elected, he would be the best friend of India in the White House.

The Houston event will be Modi's third major address to the Indian-American community after he became the prime minister in 2014 and the first after his re-election in May.

The previous two were at the Madison Square Garden in New York in 2014 and the Silicon Valley in 2016. Both the events were attended by more than 20,000 people.

The event is being organised by non-profit Texas India Forum, a recently-formed representative body of hundreds of Indian-American organisations in Texas and other parts of the US.

'Howdy', short for 'How do you do?', is a friendly greeting commonly used in southwestern United States.

Senior Democratic congressman Steny Hoyer would also join Modi and Trump for the event.

In an unprecedented show of solidarity for strong India-US relationship, over 60 prominent US lawmakers have confirmed to attend event.

Senior leaders who are expected to attend the event include US senator for Texas John Cornyn, senator Ted Cruz, congressman Al Green, US representative Pete Olson, congresswoman Sheila Jackson Lee, US representative Sylvia Garcia, and Texas governor Greg Abbot.