Protesters from one of Ghana's biggest slums clashed with police in the capital Accra on Monday, after city authorities demolished shanties as part of measures to combat heavy flooding.

Riot police fired teargas at the demonstrators from the Old Fadama slum, popularly known as Sodom and Gomorrah, and about 20 people were arrested during the altercation.

A number of officers were also injured, police said.

The clashes came after Accra's mayor, Alfred Vanderpuije, ordered bulldozers into the slum on Saturday following devastating flooding that hit the city earlier this month.

Ghana's President John Dramani Mahama blamed illegal construction near open, public drains for causing rainwater to overflow, as well as rubbish blocking the watercourses.

An estimated 60,000 people live in Old Fadama, which is not far from the scene of a deadly blaze that engulfed a petrol station, causing an explosion on June 3.

Some 150 people were killed in the inferno and due to the flooding.

The slum clearance at the weekend left thousands homeless and residents took to the streets and marched to parliament, smashing a bus, breaking flower pots and briefly occupying the building.

"We need help. This is where we work to find food and money to send to our parents in the village," one resident, Alhasan, told reporters.

"We've lost our properties. This is where I find food for my family and children, now they have destroyed everything," said another, who gave his name as Muhammed.

Vanderpuije was unrepentant, accusing the slum residents of contributing to the blockage of a major lagoon, where water flows into the sea during heavy, seasonal rains.

"It is not safe for the people who are living in those structures because given the level of rain and flooding we had, if we should have a second my fear is that the structures in which they are living can all be washed away," he said.

"Hundreds of people could be washed away... Because of the nature of their construction, water cannot flow through the Odo (river) into the Korle (lagoon) and ultimately into the ocean."

Old Fadama, also called Agbogbloshie, has in recent years become a tourist destination in its own right and featured in guidebooks such as Lonely Planet.

Lonely Planet describes it as "one of the city's most deprived, but also innovative, areas" where locals recycle old machinery, including electronic waste from around the world.

It earned its nickname of "Sodom and Gomorrah" because of its harsh living conditions and high crime rate.