Flags flew at half mast in Ghana on Monday as three days of mourning began to honour more than 150 killed in a petrol station fire during heavy flooding in the capital, Accra.

The government asked the public to wear black as a mark of respect to those who died, as the Red Cross said that 9,250 people have been affected by both tragedies.

President John Dramani Mahama will attend a service in memory of the victims on Wednesday near the site of the fire at Kwame Nkrumah Circle, his office said in a statement.

The government said it has begun to distribute relief materials, including food, water and non-food items to those hit.

"We have been able to identify a total of 9,250 people who were affected by the flood and fire, 1,125 houses were damaged while 67 people were hospitalised as of the weekend," Red Cross disaster management coordinator Francis Obeng told AFP.

A final death toll and full assessment of damages caused by the disaster is expected in about a month's time, he added.

UN agencies have been drafted in to work with national bodies helping those affected by the tragedy, which Mahama described as "catastrophic and almost unprecedented".

A fire and explosion at the Ghana Oil Company (GOIL) filling station on Thursday killed scores of people seeking shelter from torrential rains that caused widespread flooding.

The fire is thought to have spread from a nearby residence and destroyed a nearby pharmacy and several neighbouring buildings.

At least two days of heavy rains last week left many suburbs submerged and people stranded, with roads blocked and cars swept away or overturned by the flood waters.

Rainwater filled open drains blocked with rubbish and waste, causing them to overflow, according to locals.