Google's Transparency Report pages showed traffic to Google services pages from the country, embroiled in a civil war that has lasted more than two years, suddenly stopping shortly before 3 p.m. EDT (1900 GMT).
The vast majority of websites within Syria were rendered unreachable as well, other experts said, as the county appeared to shut itself off.
"Effectively, the shutdown disconnects Syria from Internet communication with the rest of the world. It's unclear whether Internet communication within Syria is still available," wrote Dan Hubbard, chief technology officer at infrastructure services firm OpenDNS.
"Although we can't yet comment on what caused this outage, past incidents were linked to both government-ordered shutdowns and damage to the infrastructure, which included fiber cuts and power outages."
Hubbard wrote on an OpenDNS blog that a similar Internet blackout in Syria occurred in November and lasted three days. About 80 Internet pathways normally are listed by Syrian providers, but only three were being advertised to machines searching for connections late on Tuesday.The Syrian ambassador could not immediately be reached for comment.