Nigerian doctors in state-run hospitals began an indefinite strike on Monday to demand a pay rise, better welfare and adequate facilities, union leaders said.

The industrial action by the National Association of Resident Doctors (NARD), which represents some 40 percent of doctors, is the latest in a string of stoppages by medics to hit Africa's most populous nation as it struggles to curb the spread of the coronavirus.

"We have kicked off the strike today," NARD president Aliyu Sokomba told AFP, adding that medics treating virus cases would join the action this time around.

"There will be no exemptions," he said.

Sokomba said long-standing issues such as provision of life insurance, a pay rise, payment of salary arrears as well as provision of adequate facilities for doctors were the reasons for the strike.

"We have arrears of 2014, 2015, 2016, salary shortfalls that were supposed to have been paid over six years ago, still pending," he said. 

"These are the issues we have and they appear not to have been addressed up till this day," he said.

"It is an indefinite strike," Sokomba said, adding that it would be called off only when the union's demands were met.

Strikes by medics have been common in Nigeria where the health sector is underfunded. 

The authorities fear any reduction in capacity could severely hamper its ability to tackle the pandemic as the number of cases continues to rise.

In June, NARD staged a week-long strike over welfare and inadequate protective kits but doctors treating virus cases remained on the job.

Nigeria, Africa's most populous nation of 200 million inhabitants, has recorded over 55,000 Covid-19 cases and 1,057 deaths.