Sri Lanka's World Cup-winning cricket captain Arjuna Ranatunga and fellow ex-skipper Sanath Jayasuriya have joined street protests demanding the president step down over the country's economic crisis.

Cricket is avidly followed in the Indian Ocean island nation and the pair called on other former players to support attempts to oust President Gotabaya Rajapaksa.

The island nation is in the grip of its worst economic crisis since independence in 1948, with severe shortages of essential goods and regular blackouts causing widespread misery.

"Cricket is driven by spectators," Ranatunga said outside Rajapaksa's office in Colombo on Friday, surrounded by demonstrators who have been protesting daily for the president's removal since last week.

"Our fans are on the streets today because they no longer can bear the hardships. We must be with our fans when they need us most. Sports stars must physically join the protests."

Hours later, his fellow former captain Sanath Jayasuriya, known as "Master Blaster", climbed the barricades in front of Rajapaksa's colonial-era office and pledged solidarity.

"Your message is loud and clear," he told the tens of thousands of protesters. "I hope the authorities will listen and ensure a brighter future for all of us."

Crowds have been chanting "Gota go home, go home Gota."

The pair are the first former captains to join the street protests in person, but other stars have previously voiced their support.

Former captain Mahela Jayawardena has strongly backed the demonstrations on social media and urged Rajapaksa to go while ex-captain Kumar Sangakkara has issued more guarded statements.

Protesters have taken to the streets daily in Sri Lanka to protest the island nation's crippling economic crisis under the administration of President Gotabaya Rajapaksa
Protesters have taken to the streets daily in Sri Lanka to protest the island nation's crippling economic crisis under the administration of President Gotabaya Rajapaksa AFP / Jewel SAMAD

Former Test player and International Cricket Council match referee, Roshan Mahanama, who has supported the anti-Rajapaksa campaign from its inception, compared the country's plight to Robert Mugabe's Zimbabwe.

"When I used to go to Zimbabwe many years ago, I saw the economic hardships people suffered there," Mahanama told AFP.

"My driver had to stand in a queue for hours to get diesel. I thought this will never happen in my country. But today we are in the same boat."

Police tightened security around Rajapaksa's office on Saturday as demonstrations demanding his resignation entered a second week.

More than a dozen trucks were seen parked near the building at the Galle Face Promenade, which is being protected by commandos and anti-riot police.

Official sources said authorities feared protest numbers could swell next week, when more marches are scheduled.

"We can expect more people to pour in. The current strength (of police) may not be sufficient," one official told AFP, asking not to be named.

"So far, the crowd is peaceful, but we can't take a chance."

Sri Lanka imposed fuel rationing on Friday in the latest effect of the crisis.

The government has urged citizens abroad to donate foreign exchange to help pay for desperately needed essentials.

It has announced a default on its entire external debt, and will open negotiations with the International Monetary Fund to seek a bailout.