Results from the 239 constituencies have been dropping more slowly than expected, leading to a second day of clashes between opposition supporters and riot police as a result of protesters angry at the delay in some results and its credibility in the commercial capital Dar es Salaam.

"We are concerned by any delays in the announcement of the results as this creates both uncertainty and suspicion among the electorate and we have concerns about the transparency of the aggregation process," said chief European Union observer David Martin.

Earlier, the defeated candidate in the presidential contest on Tanzania's semi-autonomous islands of Zanzibar said the vote was unfair but accepted a position in a coalition government to avoid the bloodshed that has marred the last two ballots.

According to Reuters, Tanzania has enjoyed relative stability in an often unsettled region and has managed to hold three successive multi-party presidential elections since 1995, after more than three decades of one-party rule.

The election is seen as a test for the ruling party's dominance in Tanzania, which has been struggling with poverty and underdevelopment. Government critics say poverty remains widespread among the majority of the population of 40 million.

Trading on Tanzania's currency market was subdued on Tuesday, with the shilling stable against the dollar, waiting for direction once the new government comes in, traders said.

Early confirmed figures gave incumbent President Jakaya Kikwete of the ruling party's Chama Cha Mapinduzi (CCM), who is seeking a second and final term, the advantage, but some political analysts expected the margin of victory to be tight.

The CCM's campaign manager Abdulrahman Kinana said his party would likely lose 51 assembly seats but win the overall vote.

"We acknowledge that the National Electoral Commission has the mandate to announce election results, but we can confirm that CCM are on course to comfortably winning the presidential and parliamentary elections," he told reporters in the commercial capital, Dar es Salaam.

Opposition making gains

The Chadema party, whose presidential candidate Willibrod Slaa campaigned hard on an anti-corruption platform, appeared to be making the most gains.

"These results are giving the impression right from the beginning that the CCM presidential candidate is leading. I think CCM has preached to itself the idea that it will win with a large margin. This might cause trouble later on," said political analyst Azaveli Lwaitama.

The EU observer group praised the peaceful conduct of the ballots but said the trappings of office had given Kikwete greater campaign visibility than his opponents.

Final presidential results are due out by Friday at the latest, the National Electoral Commission said.

Confirmed results from 53 of the 239 constituencies showed the CCM had 33 seats in the assembly but several ruling party candidates, including four cabinet ministers, were voted out.