Two crowd stampedes, one in the capital Abuja and another in the southern town of Okija, have killed "many" people, the Nigerian president's office said Saturday, days after a similar tragedy.
Both of the latest incidents happened during the distribution of food.
President Bola Tinubu cancelled his official events for the day, offering his condolences to the victims.
But he also called on the authorities to crack down on "operational lapses" by those organising such activities.
A statement from the president's spokesman said Tinubu had "cancelled all his official events in Lagos today..., in honour of the stampede victims."
"The two tragedies claimed many lives and left many others injured," the statement added.
Ten people had been killed in Abuja, including at least four children, said police spokesperson Josephine Adeh. Another eight person had been injured, she added.
"Many others" died in Okija, said police.
The Abuja stampede occurred outside the Holy Trinity Catholic Church in the Maitama district, where a food distribution drive for "vulnerable and elderly people" was underway, police said.
The Okija stampede also happened during food distribution at a community centre, as people handed out rice, said Ngozi Echeazu, an official with the National Emergency Management Agency in the south.
'Operation lapses'
"In a season of joy and celebration, we grieve with fellow citizens mourning the painful losses of their loved ones. Our prayers of divine comfort and healing are with them," said Tinubu.
But he also noted the similarities between the two incidents, and another deadly incident earlier this week in the southwestern city of Ibadan.
A stampede on Thursday at a school funfair there killed 35 children and seriously injured six others.
"Local and state authorities should no longer tolerate operational lapses by organizations and corporate bodies involved in charitable and humanitarian activities," said Tinubu.
Zubaida Umar, Director General of Nigeria's National Emergency Management Agency (NEMA), had a similar message.
A statement posted by the agency said she had "called for proper crowd management during the distribution of charity to prevent stampedes and avoidable loss of lives".
Umar was concerned that such tragedies undermined the goodwill generated by such work, "turning acts of kindness into sources of grief due to poor planning and crowd control", the agency added.
"While sympathizing with the families of the deceased and those injured, she urged organizers of similar events to engage professionals and seek the support of security agencies to manage crowds effectively," said the statement.
Police have already arrested eight people involved in organizing the school funfair at Ibadan, said Adewale Osifeso, spokesman for the force in Oyo State.