Police have announced they will search the premises of all schools on Sunday.
Sri Lanka President Maithripala Sirisena said on Saturday the security forces would "eradicate terrorism" following devastating suicide attacks on Easter Sunday and restore stability before a presidential election due by year-end.
Sri Lanka Tourism Development Authority Chairman Kishu Gomes said that based on information available, arrivals are expected to fall 60 percent in May.
Sri Lanka's main worldwide airport is located in the area, but police said there was no disruption.
Authorities in Sri Lanka have blamed the blasts on two previously little-known local Islamist groups - National Thowheed Jamath and Jamathei Millathu Ibraheem - whom they suspect had global links.
The minister did not give the nationalities of those who have been expelled, but police have said many foreigners who have overstayed their visas since the Easter attacks were from Bangladesh, India, Maldives and Pakistan.
Islamist militants said to be linked to the deadly 21 April Easter Sunday terror attacks across Sri Lanka that claimed over 250 lives and injured another 500 are said to have practised shooting and bomb-making skills in the camp.
There were tensions in the area after the Easter day attacks when one of the churches in the area became the target.
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We received assistance from numerous fire departments, police departments and our public works crews even assisted at the scene. Of the surviving employees, four were transported to area hospitals and two declined medical treatment.
He said at least one police officer will be assigned to each school for this objective.
Some 257 people were killed in a string of suicide bombings against three churches and three luxury hotels on April 21. Catholic churches were closed for a second weekend, and some Muslims have been subjected to hate comments on social media.
Asked why the threats were not taken more seriously after receiving information from India, Senanayake said: "We had some information and intelligence-sharing, situations and military intelligence on a different direction and the others were different and there was a gap that everybody could see today".
For Monday, May 6, the government had made a decision to resume lessons in public schools.
Sri Lanka's 22 million population is mostly Buddhist but includes minority Christians, Muslims and Hindus.
There were more cancellations than bookings for hotels on the island following the Easter bombings.
Nine suicide bombers, including a woman, carried out the series of blasts.