Visitors enjoying the Easter weekend at the beach were on Friday ordered to leave the shoreline at 6pm over terrorist threat.
Kenyans were also cautioned to be careful when visiting shopping malls, places of worship, government buildings and recreational centres.
On Thursday evening, Police Commissioner Matthew Iteere issued a terrorist alert and asked Kenyans to be “vigilant” wherever they were during the Easter festivities.
He said the police had intelligence report indicating that the Somali-based terror group, al-Shabaab planned to attack certain targets in highly populated areas.
“As part of community policing, we are advising the management of all the places mentioned and other places where a large number of people are admitted to enhance their security measures,” he said.
The commissioner said the police were alert and had improved security in and around the possible targets.
At the Jomo Kenyatta public beach in Mombasa, Mr Levis Juma Malove, a Kenya Maritime Authority search and rescue officer, said a siren would be sounded at 6pm every day to get people out of the water.
This timeframe will affect the stretch from Jomo Kenyatta public beach to Severin, Mombasa Beach to Reef Hotel in the North Coast and the Shelly Beach stretch in the South Coast.
The beach emergency rescue centre will operate between 10.30am and 6.30pm every day during the Easter period.
At the Likoni ferry, the anti-terrorist police unit conducted an impromptu search on passengers and motorists on Thursday.
The security agents used two sniffer dogs to check people’s luggage and vehicle boots in the channel used by 250,000 people and more than 3,000 vehicles daily.