The Sri Lankan Defence Secretary Hemasiri Fernando has announced that he has resigned, taking responsibility for the suicide bomb attacks on the country last Sunday.

He told Reuters that while there had been no failure on his own part, he was taking responsibility for failures of some institutions he headed as the secretary of defence.

He said that security agencies were actively responding to intelligence they had about the possibility of attacks before they were launched.

"We were working on that. All those agencies were working on that," he said.

The Easter Sunday bombings on churches and luxury hotels killed at least 359 people and wounded around 500 others.

Meanwhile, Sri Lankan authorities locked down the central bank and shut the road leading to the capital's airport today due to a bomb scare.

Two bank officials told Reuters the street outside the building near the World Trade Center in the capital, Colombo, was blocked to traffic before the security alert was lifted.

Underscoring the nervous atmosphere in the Indian Ocean nation, authorities also shut the entry road to Colombo's main airport after a suspicious vehicle was spotted at a car park.

The road was reopened when the alert was declared a false alarm.

A police spokesman also said there was an explosion in a town east of the capital but there were no casualties. The cause was not clear but it was not a controlled detonation like other blasts in recent days and was being investigated, he said.

With fears of more bombers ready to strike, police said they had asked people to leave offices early in Colombo's business district to avoid throngs at rush hour. City centre restaurants were also shutting early.

More people, including foreigners, were arrested for questioning overnight as domestic and international authorities investigated Sunday’s bombings, believed to have been the deadliest such attack claimed by Islamic State.

Police said 16 people were detained for questioning overnight, taking the number held since Sunday to at least 76.

They include a Syrian national, detained after police got information about him from Sri Lankan suspects.

The government said there were nine suicide bombers, eight of whom had been identified, and one was a woman.

Australian Prime Minister Scott Morrison said another one of the bombers had lived in Australia with his wife and child on a student visa but left in 2013.

Here, the Department of Foreign Affairs is advising people to avoid non-essential travel to Sri Lanka following the weekend bombings. 

The Department said it regularly reviews its Travel Advice based on the reports from Irish missions, local contacts, EU partners and a wide range of other sources.

People who do travel to Sri Lanka are advised to avoid large crowds and public spaces, and to stay indoors where possible.

They are also advised to co-operate with local security forces and monitor local news.