Maldives' parliament has approved the extension of a state of emergency by 30 days, in a vote the opposition condemned as "illegal".

The move on Tuesday comes amid continuing protests in the capital, Male, and widespread international condemnation of the initial 15-day emergency imposed by President Abdulla Yameen on February 5.

Yameen had cited threats to national security after the Supreme Court overturned criminal convictions against nine of his opponents and ordered their release.

He sent the army to storm the Supreme Court building and arrest the island nation's chief justice and another judge on the top court's bench. His estranged half-brother, former President Maumoon Abdul Gayoom, who has sided with the opposition, was also arrested.

The three remaining judges on the Supreme Court then reversed part of their verdict on the release of Yameen's opponents.

Later, judges also revoked the reinstatement of 12 parliamentarians who were stripped of their seats for defecting to the opposition.

The crisis prompted near-daily protests by opposition supporters and resulted in sporadic clashes between protesters and police.

Two journalists were assaulted by riot police during a protest on Friday.

Key tourist markets, including China and the UK, also issued travel advisories to the upmarket holiday destination.

The 15-day emergency was set to expire on Tuesday, and Yameen asked the parliament on Monday to extend it by another 30 days "due to the present threat to national security and constitutional crisis" caused by the Supreme Court ruling, according to a statement by his office.

The opposition boycotted Tuesday's vote, and the emergency extension was approved, with 38 ruling party legislators voting in favour.

In a statement, the opposition said the extension was "illegal and void", citing a constitutional provision that requires 43 members of the 85-member house to be present in the chamber when voting on a matter of public compliance.

However, Speaker Abdulla Maseeh, introducing the vote on Tuesday, said parliamentary regulations do not require the constitutionally mandated quorum in order to extend a state of emergency.

In a statement, Ibrahim Mohamed Solih, leader of the opposition parliamentary group, said: "President Yameen failed to muster the required number of votes to pass his emergency legislation. And so Yameen has ratified and extended the emergency illegally.

"President Yameen has, in effect, hijacked the entire state and is ruling the Maldives like a military dictator."

Earlier in the day, India's foreign ministry urged Yameen against the move.

"It is our expectation that the Government of Maldives will not be seeking extension of the State of Emergency so that the political process in the Maldives can resume with immediate effect," it said in a statement.

The UN human rights chief called the emergency an "assault on democracy" earlier this month.