The Remote Gambling Act passed through parliament in October and took effect on Monday, giving the government broad powers to block access to overseas gambling portals as well as stop electronic payments to their operators.
A spokesman from the home affairs ministry told AFP that "several hundred remote gambling websites have been blocked".
Popular gambling websites based abroad such as Paddy Powers, ibcbet.com and sbobet.com were not accessible on Tuesday afternoon from Singapore, one of Asia's most wired states.
"Viewing and using this website at your current location is prohibited due to its regulatory rules," said a message when ibcbet.com was accessed via a Singapore IP address.
Under the law, exemptions can be granted for locally based online gambling operators that follow strict rules and operate on a non-profit basis. Lottery operator Singapore Pools told local media it would apply for the exemption.
Singapore currently bans access to about 100 websites, mostly featuring pornographic, extremist and hateful content. Access to extramarital dating site Ashley Madison is also banned in the city-state.
The new law will make it an offence, punishable by jail terms and fines, for people to place bets on overseas gambling websites from Singapore, while advertisements for them on online and offline platforms will also be outlawed.
In a statement last year, the home affairs ministry said the objective of the law was to "maintain law and order and protect young persons and other vulnerable persons from being harmed or exploited by remote gambling".
Media and technology experts have said the prevalence of virtual private network (VPN) usage among Singaporean users could erode the effectiveness of the restrictions.
But authorities have also threatened to block websites of VPN service providers that offer services openly aimed at bypassing the ban on remote gambling.
Sports betting, especially on top European football league matches, is deeply entrenched in wealthy Singapore. Its online gambling market is estimated to be worth US $416 million (roughly Rs. 2,568 crores), with 95 percent of revenues headed towards overseas websites, Singapore's Straits Times reported last year.