The facilities were attacked in retaliation after days of riots in South Africa chiefly targeting foreign-owned, including Nigerian, businesses.
The change means the minimum monthly wage will rise to 30,000 naira ($98) from 18,000 now, said aide Ita Enang, a senior special assistant to the president on the National Assembly.
Buhari faces a tight contest against Atiku, a business and ex-vice president, in Saturday’s election in Nigeria, Africa’s biggest democracy.
Donatus Mwamkpa, APC chairman in the southwestern Abia State, was seized by gunmen on Monday, "a few hours" before Buhari's arrival for a rally, police spokesman Geoffrey Ogbona said.
Atiku Abubakar was a notable absentee at Tuesday's ceremony in Abuja, at which President Muhammadu Buhari and dozens of other candidates vowed to ensure non-violence.
May says she wants to see strong African economies that British companies can do business with in a free and fair fashion.
Clashes between semi-nomadic herders, mostly of the Fulani ethnic group, and settled farmers in central states have killed around 100 people in recent weeks.
Campaigning for the re-election of a president in Nigeria has often started with such support groups before the incumbent declares his intention to run again.
Zimbabwe’s protest pastor Evan Mawarire says citizens in that country must play their part in standing against the current government and bring about positive change.
