Several American senators have called for an investigation into whether US President Donald Trump engaged in insider trading or market manipulation by encouraging people to buy stocks just before his dramatic reversal on global tariffs.

"Who in the administration knew about Trump's latest tariff flip flop ahead of time? Did anyone buy or sell stocks, and profit at the public's expense?" California Democratic Senator Adam Schiff posted on X on Wednesday.

"I'm writing to the White House – the public has a right to know," he added.

Democratic members of the House Financial Services Committee wrote on X that "the President of the United States is literally engaging in the world's biggest market manipulation scheme."

The accusations came as Trump posted a few minutes after Wall Street opened that "IT'S TIME TO BUY".

A few hours later, he announced a 90-day suspension of additional tariffs against dozens of countries, with the exception of China, triggering a historic stock market rebound.

After several days of collapse, the Dow Jones index ended Wednesday up 7.87 percent, its biggest gain since 2008, and the Nasdaq up 12.16 percent, the most since 2001.

Trump also signed his post on Truth Social with the letters "DJT" – both his initials and the stock market abbreviation for his media company, Trump Media & Technology Group. The company's shares closed the day up 21.67 percent. (AFP)