* Zambian election results trickle in
* Large voter turnout at polling stations
* Opposition candidate in early lead (Updates results)
By Chris Mfula
LUSAKA, Aug 14 (Reuters) - Opposition leader Hakainde Hichilema extended his early lead over long-time rival and incumbent Edgar Lungu in Zambia's presidential election on Saturday, results announced by the electoral commission showed.
Lungu, 64, has been in power since 2015. Hichilema - known as "HH" - is a businessman who has criticized the president's management of an economy in turmoil.
Investors are closely watching the outcome of the election, which was held on Thursday: the southern African country is highly indebted and suffered the continent's first pandemic-era sovereign default in November.
International Monetary Fund (IMF) support, already broadly agreed, is on hold until after the vote. So too is debt restructuring seen as an early test of a new global plan to ease the burden on poor countries.
Results from 31 of the country's 156 constituencies gave Hichilema 449,699 votes versus the 266,202 garnered by Lungu, who is running for a second five-year term.
Some constituencies include perceived Lungu strongholds, suggesting Hichilema has gained ground since the last elections in 2016, when he lost by a slim margin in elections marred by allegations of rigging.
The first results had initially been expected on Friday. They were delayed after counting went on overnight following a heavy turnout and because political parties objected to the electoral commission’s initial figures in one constituency, which differed with those from monitors on the ground.
An estimated 7 million people registered to vote in the presidential and parliamentary elections in Zambia, Africa's second biggest copper producer.
SOCIAL MEDIA RESTRICTIONS
The Electoral Commission of Zambia allowed the last polling station to remain open until 5 a.m. on Friday to give people who had queued for hours an opportunity to vote. The election also saw violence in three regions and restrictions on internet access.
In Chawama township in Lusaka, Lungu’s parliamentary constituency before he became president, residents said supporters of both Lungu and Hichilema both claimed victory and celebrated throughout the night.
Lungu's ruling Patriotic Front party said its vote tally showed a huge turnout in its strongholds and it was confident of victory.
Hichilema is running for the United Party for National Development.
Following a complaint lodged by local human rights' organization, Chapter One Foundation, a high court on Friday overturned a decision by the government regulator to block social media platforms including WhatsApp, Facebook and Instagram.
Linda Kasonde, the Foundation's executive director, said it was unclear how long the social media internet blackout would remain in force. Some people said on Saturday their online services were back up.
"It did go up. Some people reported that WhatsApp went down but they had access to Facebook and Twitter," she said.
According to the court ruling seen by Reuters, the Zambia Information Communication Technology Authority ordered the block on Thursday, the day of the election.
Richard Mulonga, chief executive of Bloggers of Zambia, an independent group, said it was unclear whether the national regulator had implemented the order and that it could take "a week or even months" for services to stabilize.
Lungu has cast doubt on the outcome of the election in three provinces after accusing the opposition of stirring violence on Thursday that killed an official from the ruling party.
He directed the army to send reinforcements to the provinces on Thursday. However, European and African observers said the vote had been largely peaceful. (Reporting by Chris Mfula, Writing by Wendell Roelf Editing by William Mallard, Frances Kerry and Timothy Heritage)