Voters wait in line at a polling station in Kampung Baru for the 14th general election on May 9, 2018 in Kuala Lumpur, Malaysia. Millions of Malaysians headed to the polls on Wednesday in a fiercely contested general election between the ruling coalition of Prime Minister Najib Razak and 92-year-old former leader Mahathir Mohamad.

Malaysian politicians from both government and opposition camps complained of "dirty tricks" after voting in a general election began on Wednesday, as non-stop spam calls to their mobile phones disrupted communications with party organizers.

Malaysian civil rights group Suaram said the spam calls, which have also affected civil society group leaders, was a "clear attempt to impede the work of human rights defenders and politicians at the critical juncture of voting day".

The election is arguably the toughest faced by Prime Minister Najib Razak's ruling Barisan Nasional coalition, as it contends with a resurgent opposition pact led by former strongman Mahathir Mohamad.

While the complaints came from all sides, none of the political figures whose phones had been targeted specified who they suspected was behind the attack.

Najib condemned the "spam calls" received by BN leaders, and said that many of the coalition's websites could not be accessed.

"I have ordered for immediate action to be taken," the prime minister said on Twitter.

Some leaders from the opposition Pakatan Harapan (PH) coalition said they had switched off their phones after receiving automated calls nearly every minute from mostly unknown overseas numbers, since before polling stations opened.

"This is a dirty tech attack on us, we have been paralysed. We cannot talk to anyone... they are trying to sabotage the electoral system to deny a PH win," said Lim Guan Eng, a senior opposition leader.

"The telcos must do something. We can complain to the authorities, but what can they do now?" Lim said.

A minister in Najib's government said his phone had also received multiple calls from unknown numbers from the United States, the U.K. and Malaysia, while another ruling coalition leader posted a video on twitter showing a phone receiving call after call.

The Malaysian Communication and Multimedia Commission (MCMC), the country's communications regulator, did not respond immediately to requests for comment.

Azmin Ali, the chief minister of the opposition-held state of Selangor, said he left his mobile phone in his car when he went out to vote as he was getting continuous calls and junk emails.

"They are desperate, so they are using all sorts of tactics to jam us. But at the end of the day, it's people's power," he told reporters after casting his vote.

Khairy Jamaluddin, the sports minister and youth wing leader of the United Malay National Organisation (UMNO), which leads the ruling coalition, was among the leaders from the government side that said they had been targeted too.

"My phone seems to be under some sort of spam attack this morning," said Khairy, displaying on his Twitter account a screenshot of a list of calls received. "Strange." Abdul Rahman Dahlan, a ruling coalition leader, posted a video showing a phone receiving endless calls.

"Calls from overseas keep coming in every few seconds! To prevent us from communicating with our machinery. This is dirty trick!" he said in a Twitter post.

Reuters reported in April that automated accounts known as bots were flooding Twitter with tens of thousands of pro-government and anti-opposition messages, just weeks before the general election.

A survey by independent pollster Merdeka Center showed BN has seen a drop in its share of the popular vote, but was still expected to win enough parliamentary seats to retain power.