Human rights groups have condemned the "unnecessary and excessive use of force" by Kenyan police as the country imposed a dusk-to-dawn curfew amid efforts to slow the spread of the new coronavirus.

On Friday, police fired tear gas at a crowd of ferry commuters in the port city of Mombasa before the 19:00 to 05:00 curfew came into force, 20 human rights groups, including Amnesty International, said.

This allegedly forced hundreds of people to touch their faces as they vomited, spat and wiped away tears, increasing the chance of the virus's spread, the organisation said.

Some health workers even reported being intimidated by police officers as they tried to provide services after the curfew, according to the rights groups.

Captured

Elsewhere, officers were captured in mobile phone footage beating people with batons, causing uproar in the country.

"We continue to receive testimonies from victims, eyewitnesses and video footage showing police gleefully assaulting members of the public in other parts of the country," the rights groups said.

Kenya's interior ministry on Saturday replied to the criticism in a statement saying the curfew "is meant to guard against an apparent threat to public health. Breaking it is not only irresponsible but also puts others in harm's way".

The guidelines issued to security forces on the curfew say that police can use "proportionate force where non-violent means are inadequate to achieve the objectives of the curfew".

The government has not said how many people have been arrested. Because courts are also affected by the virus prevention measures, all but serious cases will now be dealt with at police stations, the government has said.

That means anyone detained for violating curfew faces time in crowded cells.

Kenya has so far confirmed 38 cases of the new coronavirus, which causes a highly infectious respiratory disease called COVID-19. The country has taken a series of measures to stop its spread, including shutting borders and banning most air travel.