Riyadh took the lead on Monday to sever relations and other countries fell in line after an official source said the kingdom "urges all brotherly countries and companies to do the same."
A Saudi official cited by SPA said the country decided to "sever diplomatic and consular ties with Qatar, and to close all land, sea and aviation ports" in order to "protect its national security from the dangers of terrorism and extremism."
The "decisive" measure, the Saudi statement said, was due to "gross violations committed by authorities in Qatar over the past years."
Qatar's foreign ministry said it regretted the measures by the Arab nations, calling the decisions "unjustified".
"The measures are unjustified and are based on claims and allegations that have no basis in fact," the statement said, adding that the decisions would "not affect the normal lives of citizens and residents".
The United Arab Emirates gave Qatari diplomats 48 hours to leave the country, citing their "support, funding and embrace of terrorist, extremist and sectarian organizations," state news agency WAM reported.
Bahrain news agency said the tiny kingdom was cutting ties with Doha over its insistence on "shaking the security and stability of Bahrain and meddling in its affairs."
Egypt accused Qatar of supporting "terrorist" organizations, including the Muslim Brotherhood which it has been cracking down on since the 2013 coup against the country’s first ever democratically-elected leader, Mohamed Morsi.
Meanwhile, a Saudi "coalition" waging a war in Yemen said it was ending Qatar's membership. The measure, it said, was due to Doha's "practices that strengthen terrorism, and its support to organizations in Yemen, including al-Qaeda and Daesh, as well as dealing with the rebel militias."
The crisis follows US President Donald Trump’s visit to the region last month, marked by the signing of a $110-billion arms deal with Saudi Arabia.
US Secretary of State Rex Tillerson said the visit was aimed at getting Saudi Arabia and other Arab nations in the region to stand in “unity” with Israel and confront Iran.
Tensions have escalated between Riyadh and Doha since an article appeared on Qatar’s state-run news agency late in May, quoting the emir as criticizing the United States, Saudi Arabia, and their client states for attempting to stir up tensions with “Islamic power” Iran.
A post also appeared on the agency’s Twitter page, quoting the Qatari foreign minister as saying that his country was withdrawing its ambassadors from Kuwait, Bahrain, Egypt, Saudi Arabia, and the UAE amid tensions.
The Qatari government soon said the state agency had been hacked and that the remarks attributed to the emir and the foreign minister had never been made.
The official denial, which was offered several more times, nevertheless failed to stop the rift between the Persian Gulf Arab countries from widening.
Saudi media viciously attacked Qatar, accusing it of having “betrayed” the other Arab countries particularly at a time when they had attempted to stage a show of “unity” against Iran in a much-publicized and extravagant series of events in Riyadh.
Saudi Arabia and the United Arab Emirates also blocked Qatari websites and broadcasters. Qatari Foreign Minister Mohammed bin Abdulrahman Al Thani later said the country was being targeted in a “hostile media campaign, which we will confront.”