Sri Lanka's former president, Gotabaya Rajapaksa, is expected to arrive in Thailand on Thursday and stay temporarily in a second Southeast Asian country since fleeing his island nation last month in the midst of mass protests.

Rajapaksa fled to Singapore on July 14 and resigned from office shortly afterwards, following unprecedented unrest over his government's handling of the worst economic crisis in seven decades, and days after thousands of protesters stormed the president's official residence and office.

The former military officer, who is the first Sri Lankan head of state to quit mid-term, is expected to travel from Singapore to Thailand's capital of Bangkok on Thursday, two sources said. It was unclear what time he would arrive.

Thai authorities said Rajapaksa had no intention of seeking political asylum and would only stay temporarily.

"This is a humanitarian issue and there is an agreement that it's a temporary stay," Prime Minister Prayuth Chan-ocha told reporters on Wednesday.

Prayuth also said Rajapaksa could not participate in any political activities while in Thailand.

Foreign Minister Don Pramudwinai said the current Sri Lankan government supported Rajapaksa's trip to Thailand, adding that the former president's diplomatic passport would allow him to stay for 90 days.

Rajapaksa has made no public appearances or comment since leaving Sri Lanka, and Reuters was not able to immediately contact him.

Sri Lanka's economic crisis is a result of several factors including COVID-19, which battered its tourism-reliant economy and slashed remittances from workers overseas, rising oil prices, populist tax cuts and a seven-month ban on the import of chemical fertilisers last year that devastated agriculture.