Twitter became inaccessible on major Turkish mobile providers on Wednesday as online criticism mounted of the government's response to this week's deadly earthquake.

AFP reporters were unable to access the social media network across Turkey. It still worked using VPN services that disguise a user's location and are generally free to use.

The netblocks.org social media monitor showed Twitter becoming throttled and then completely blocked across all major cell phone providers.

"The filtering measure is likely to impact community rescue efforts underway after the series of deadly earthquakes on Monday," netblocks.com warned.

"Turkey has an extensive history of social media restrictions during national emergencies and safety incidents," the monitor added.

Turkish police have detained 18 people since Monday's earthquake over "provocative" social media posts that criticised how President Recep Tayyip Erdogan's government has been dealing with the disaster.

The 7.8-magnitude tremor and its aftershocks killed at least 11,700 people in southeastern Turkey and parts of Syria.

The disaster has already become the deadliest of Erdogan's two decades in power -- a tumultuous era beset with an attempted coup and violent protests as well as a series of smaller earthquakes and floods.

Turkish social media have been filled with posts by people complaining about a lack of search and rescue efforts in their provinces. Officials released no immediate statements about the Twitter outage.

But they had issued repeated warnings about spreading misinformation in advance of a crucial May 14 election in which Erdogan will try to extend his two-decade rule.

Turkey's opposition leaders and celebrities warned that Twitter's absence threatened to disrupt rescue efforts and humanitarian relief work.

"Let's stop this disgrace immediately," the secular main opposition CHP party's leader Kemal Kilicdaroglu declared. "We know everything they are trying to hide."

Nationalist opposition Iyi Party chief Meral Aksener said Twitter was needed "to relay the needs of earthquake victims."

The two leaders head a six-party alliance that is trying to agree on a single presidential candidate to run against Erdogan.

But the government's apparent decision to block Twitter in the middle of a profound national crisis reverberated far beyond the Turkish political sphere.

Turkish rock star Haluk Levent -- a crooner with 7.2 million Twitter followers and his non-profit group involved in helping people in need -- tweeted: "Err, what are we going to do now?"

The Twitter outage came as Erdogan toured two of the hardest-hit Turkish provinces.

He directly acknowledged "shortcomings" in the government's handling of the disaster but pledged to redouble efforts to help the victims.

"It's not possible to be ready for a disaster like this," Erdogan said during a visit to the hard-hit Hatay province.