Doha News said both of the Gulf state's internet service providers had prevented readers reaching the site since Wednesday. It created another domain, but that too stopped working.
"We can only conclude our website has been deliberately targeted," it said.
There has so far been no comment from the ISPs or the Qatari authorities.
Qatar has enjoyed a reputation as a centre for media freedom, owing in part to its funding and hosting of the Al Jazeera news network.
But last year the authorities detained two groups of foreign journalists from the BBC and West German Broadcasting, as they attempted to report on the treatment of migrant workers as the country prepares to host football's World Cup in 2022.
Doha News has been operating for almost eight years and says it has an audience of almost one million unique users a month.
In a statement posted on its website on Thursday, Doha News said its domain had become inaccessible to most online users in Qatar on Wednesday after apparently being blocked simultaneously by the country's two ISPs, Ooredoo and Vodafone.
While it put in requests for information from the authorities it temporarily diverted readers to an alternative domain. However, that also stopped working.
"Given this development and the silence from the government and ISP providers, we can only conclude that our website has been deliberately targeted and blocked by Qatar authorities," the statement said.
"We are incredibly disappointed with this decision, which appears to be an act of censorship."
"We are also puzzled because authorities did not discuss any concerns they had with us before taking such serious action," the statement added.
The AFP news agency noted that Doha News carried an editorial two months ago that alleged that Qatar's cybercrime law was being used to "silence" people.
In August, it published an article by a man on the challenges of being gay in Qatar, where "sodomy" can be punished with one to three years in prison and Muslims convicted of sex-outside marriage can be sentenced to flogging or even death.
A popular English-language news outlet in Qatar says access to its website has been blocked in an apparent act of censorship by the government.