The runaway animals galloped past bewildered Londoners going about their morning commute
A local police spokesman said 17 people, including five female suicide bombers who carried out the attacks on late Sunday, were confirmed dead.
Another four died in hospital on Monday, Xinhua news agency quoted the National Emergency Management Agency as saying.
The attackers struck near a camp of the Internally Displaced Persons at Kofa Village, located eight kilometres away from Maiduguri city, the capital of restive Borno State.
Terror group Boko Haram was suspected to be behind the blasts.
Boko Haram had been blamed for the deaths of more than 20,000 people and displacing of 2.3 million others in Nigeria since their insurgency started in 2009.