President Muhammadu Buhari has been in Britain since mid-January for unspecified medical checks and many Nigerians suspect his health is worse than officials admit.

Hundreds marched through Lagos on Monday calling for a change of government, a rare show of public dissent reflecting worry over Buhari's absence and a sputtering economy.

Some fear a rerun of the unstable three months in 2010 when then-president Umaru Yar'Adua's illness was shrouded in secrecy before he died, after which Vice President Goodluck Jonathan was sworn in.

Current Vice President Yemi Osinbajo, acting leader in Buhari's absence, told reporters in Abuja the president was "hale and hearty" when they spoke on Monday afternoon.

Buhari asked after progress of his proposed budget for 2017, which has not yet been approved by parliament, and plans for economic recovery. Nigeria is mired in its first recession in 25 years.

Osinbajo acknowledged Monday's protests, saying: "I informed (Buhari) about the protest march and feedback about what people are saying about the economy," without giving details of the president's response.

The president needed to go for more tests, as outlined in a letter to parliament on Sunday requesting extended medical leave.

"Once he sees the test results and gets medical advice, we expect him very soon," Osinbajo said.