A senior police officer said the night curfew was imposed to prevent an escalation of mob violence after attacks occurred in Negombo -- north of Colombo -- where over 100 Christians died in a church bombing two weeks ago.
"At least two motorcycles and two three-wheel taxis have been damaged in the clashes," the police officer told AFP. "We declared a curfew till 7.00 am (0130 GMT) to contain the unrest."
There were no immediate reports of casualties.
The country's main international airport is located in the area, but police said there was no disruption to airport traffic. Elite Special Task Force commandos were deployed to patrol the streets, police said.
The senior officer said an investigation was underway into the clashes, the first violence between Muslims and Christians since the April 21 jihadist attacks targeting three churches and three luxury hotels in the country.
Tensions gripped Negombo as the authorities prepared to reopen public schools after an extended Easter vacation following the suicide attacks blamed on a local jihadist group which pledged allegiance to the Islamic State group.
The country has been under a state of emergency since the suicide bombings. Security forces and police have been give sweeping powers to arrest and detain suspects for long periods.
Earlier in the day, tens of thousands of security personnel searched public schools for explosives ahead of their reopening Monday.
Foreign clerics expelle
The search for explosives and a security cordon thrown around 10,900 schools nationwide came as the government said it has expelled over 600 foreigners, including about 200 Islamic clerics, since the April 21 attacks.
Police spokesman Ruwan Gunasekera said "police and soldiers combed school premises and the surrounding areas to make sure it is safe for children to go back" on Monday.
As part of the clampdown after the attacks on three churches and three luxury hotels, the government announced a crackdown on foreign Islamic clerics operating in the majority Buddhist country.
Home Affairs Minister Vajira Abeywardena said 200 clerics were found to have overstayed visas, for which fines were imposed and they were then expelled.
"Considering the current situation in the country, we have reviewed the visas system and took a decision to tighten visa restrictions for religious teachers," Abeywardena told AFP.
"Out of those who were sent out, about 200 were Islamic preachers."
The suicide attacks were led by a local cleric who is known to have travelled to neighbouring India and made contact with jihadists there.
The minister did not give the nationalities of those who have been expelled, but police have said many foreigners who have overstayed their visas were from Bangladesh, India, Maldives and Pakistan.
"There are religious institutions which have been getting in foreign preachers for decades," Abeywardena said. "We have no issues with them, but there are some which mushroomed recently. We will pay more attention to them."
The minister said the government was overhauling its visa policy following the attacks.
House-to-house searches are being carried out across the country looking for explosives and propaganda material of Islamic extremists.