Kenyan police have offered a $10,000 (£7,600) reward to help find an Italian aid worker and the three men accused of abducting her on Tuesday.
Silvia Romano was taken by gunmen from a small rural hotel in Kilifi County in the south-east of the country.
Five people, including three children, were wounded in the attack and taken to hospital.
Police said that they were “doing all they can to rescue” Ms Romano and arrest the kidnappers.
It is not known whether the men who kidnapped the 23-year-old volunteer are members of a local gang aiming to get a ransom or are linked to the Islamist militant group al-Shabab.
The police have posted pictures of the three suspects on Twitter, describing them as “armed and dangerous”.
Twenty people have so far been arrested in connection with the kidnapping, AFP news agency reports, quoting police chief Joseph Boinett.
Ms Romano, who works for the Italian charity Africa Milele Onlus, is the first foreigner to be kidnapped in Kenya since the country had a spate of abductions that threatened its tourism resurgence in 2011.
Al-Shabab is thought to have been responsible for killing a British man and kidnapping his wife from a resort island in 2011.
A few weeks later, a disabled French woman was taken from her home on the Lamu archipelago and reportedly died while in captivity.
Two Spanish aid workers were abducted in the same year by suspected jihadist gunmen from the Dadaab refugee camp close to the Somali border.
They were freed 21 months later.