More than 150 people have died in a devastating petrol station blast during heavy flooding in Ghana's capital, prompting the nation's leader to call three days of national mourning over the "catastrophic" loss of life.

The fire hit a filling station in Accra late on Wednesday, causing an explosion at the pumps that killed dozens of people seeking shelter from torrential rains and widespread flooding in the area that also claimed numerous victims.

"As of yesterday (Thursday) we have recovered more than 150 corpses. Sixty people have been taken to the hospital," Red Cross disaster management coordinator Francis Obeng told AFP Friday, raising the toll from Thursday's count of at least 90 killed.

As he toured the scene of the disaster, Ghana's President John Dramani Mahama described the loss of life as "catastrophic and almost unprecedented" and announced three days of national mourning from Monday, with flags flying at half-mast, after rescue operations finished.

"A lot of people have lost their lives and I am lost for words," he told reporters.

- Explosion heard across capital -

The fire, which is thought to have spread from a nearby residence, appeared to have engulfed a bus full of passengers that was waiting at the station, an AFP reporter at the scene said.

Dozens of charred motorcycles and cars were visible on the forecourt.

Local residents said many people had sought refuge under the filling station canopy from days of heavy rains that have engulfed Accra.

Flood waters had reached knee level on the road beside the Ghana Oil Company (GOIL) petrol station in the Kwame Nkrumah Circle area of the city before the fire, which caused an explosion at the pumps, according to eye-witnesses.

The inferno quickly spread to a nearby pharmacy and several buildings next to the filling station.

The explosion was heard and seen across the capital. It was not immediately clear exactly how the victims died, with reports that some had drowned after being knocked unconscious and falling into the flood waters.

Obeng said rescuers as well as dozens of volunteers were currently providing relief materials to those displaced or affected by the disaster.

President Faure Gnassingbe of neighbouring Togo on Friday began a tour of the scene of the tragedy and the hospital in company of his host, Mahama.

One man at the 37 Military Hospital, Kwame Adu, said he lost eight people in the tragedy -- colleagues and friends.

- Fire service stuck -

Mahama has extended his condolences to the families of those who lost loved ones and said "precautionary measures" needed to be taken against the flooding that hits the city every year.

"Our current priority now is to save lives and prevent any further suffering of our people. Beyond that, we will take the tough measures that are necessary to prevent such disasters in the future," he said.

The GOIL filling station is next to a large open drain that carries water from surrounding areas to the sea.

But like many gutters in the city, it was blocked with rubbish, causing water to spill onto the streets. Flooding is exacerbated by construction work in the city.

One witness, Edgar Wiredu, told GTV 24 television: "Because of the construction work, the whole of (Kwame Nkrumah) Circle was flooded.

"When the fire service got to the scene, they got stuck. They struggled to gain access to the scene."

At least two days of rains have caused chaos in Accra, leaving many suburbs submerged and people stranded, with roads blocked and cars swept away or overturned by the flood waters.

Already sketchy power supplies had been cut to some communities as electricity sub-stations were under water, said communications minister Edward Omane Boamah.

"The general public is kindly advised to avoid fast-moving rainwater and areas they know have big drains. Stay on higher ground, where necessary, to prevent loss of life," he added.

Ghana police spokesman Arthur Cephas said the situation was under control.

"Police are protecting lives and properties as well as ensuring that evidence that would assist in the investigation is not tampered with," he told AFP.