Militants have killed at least 10 people in Nigeria by using rocket-propelled grenades, which local officials describe as a "new trend".
Suspected Boko Haram militants fired from the outskirts of the north-eastern city of Maiduguri into densely populated areas, according to Borno state governor Babagana Zulumon.
He said the use of these weapons "has to be stopped".
It is the worst attack of its kind in Maiduguri in a year.
The city is the birthplace of Boko Haram.
The militants came through Boboshe village, a known Boko Haram enclave, AFP news agency quotes eyewitness Sama'ila Ibrahim as saying.
They then crossed the ditch fortification around Maiduguri and started shooting sporadically which sent people scrambling for safety, he added.
Explosives began to rain down near the University of Maiduguri at around 18:00 local time on Tuesday, Reuters news agency quotes witnesses as saying.
One of the grenades hit a children's playground, Mr Zulumon said. It is not clear if any of the children are among the casualties.
The sound of gunfire died down by 19:30 as the military fought the attackers, Reuters reports.
Attack signifies a breach of city's extensive defences
By Mayeni Jones, BBC News, Lagos
This strike in the heart of the capital of Borno state is a reminder that insurgents can still cause serious harm to civilian populations.
Attacks using rocket-propelled grenades have been rare in Maiduguri, but are becoming more common.
A similar attack on the city took place in July 2020 when three rockets left four dead and three wounded.
It had a much lower death toll but suggests a pattern may be forming.
The city is heavily guarded and is seen as one of the safest places in the besieged state of Borno.
But launching bombs from a distance enables militants to reach targets that they couldn't otherwise access.
The militants' ability to strike a densely populated neighbourhood has spooked many of Maiduguri's residents and raises questions as to how they were able to breach the city's defences.
No group has yet claimed responsibility for the attack, but Maiduguri has frequently been targeted by the insurgents.
The Boko Haram insurgency, which has lasted for more than a decade, has killed at least 36,000 people and displaced two million in north-eastern Nigeria.
Boko Haram is not the only active jihadist group in the region - the Islamic State West Africa Province (Iswap) emerged as a splinter group in 2016.